China has been accused by the Philippines of reclaiming land on a reef in disputed islands to build an airstrip just days after Washington described Beijing's actions in the region as 'provocative'. If confirmed, the airstrip would be the first built by China on any of the eight reefs and islands it occupies in the Spratly Islands in the South China Sea. It would also mark a significant escalation in tensions involving several nations in the area. China claims almost the entire South China Sea, an area rich in energy deposits and an important passageway traversed each year by $5trillion worth of ship-borne goods. Scroll down for video . Outrage: Vietnamese and Filipino protesters outside the Chinese Consulate at the financial district of Makati city to protest the recent moves by China to construct an oil rig in disputed waters in the South China Sea . Location: If confirmed, the airstrip would be the first built by China on any of the eight reefs and islands it occupies in the Spratly Islands in the South China Sea . Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims on the area. Philippine . Foreign ministry spokesman Charles Jose told Reuters that China had . been moving earth and materials to Johnson South Reef, known by the . Chinese as Chigua, in recent weeks. He . said China was reclaiming land in violation of the Declaration on the . Conduct of Parties in the South China Sea, an informal code of conduct . for the region. 'They're about to build an airstrip,' Jose said. He said evidence of the Chinese activity on the reef had been shown in aerial photographs taken by the Philippine Navy. Tensions rise: Chinese coast guard vessels (right) and an unidentified naval vessel (left) near China's oil drilling rig (centre) in disputed waters in the South China Sea, off the coast of Vietnam . On patrol: Chinese coast guard vessels in the South China Sea. Beijing and Hanoi each accused the other of ramming its ships near the disputed Paracel Islands where China has moved a large oil rig . The Philippines and Taiwan already have airstrips in the area. The . ministry had already lodged a protest with the Chinese and raised the . issue behind closed doors at last weekend's summit of the Association of . South East Asian Nations in Myanmar, Jose said. Tensions in the South China Sea were already high after China moved a large oil rig into an area also claimed by Vietnam. Beijing and Hanoi each accused the other of ramming its ships near the disputed Paracel Islands. It . came as Vietnam's prime minister sent a text message to millions of . citizens urging them to act in defense of the country's sovereignty . following China's deployment of the oil rig, but said that 'bad . elements' shouldn't be allowed to engage in violence. The . message, sent late Thursday and Friday to subscribers via major . state-owned cellphone operators, didn't directly condemn the riots that . have broken out this week following China's decision to deploy the rig . off the coast of central Vietnam on May 1. Vietnam's prime minister sent a text message to millions of citizens urging them to act in defense of the country's sovereignty following China's deployment of the oil rig . On the lookout: A Vietnamese coast guard officer watches one of his vessels vessel in the South China Sea . Vietnamese patrol ships sent to disrupt the rig are currently locked in a tense standoff with Chinese ships guarding it. Anti-China protests that started . peacefully have ended in violence and vandalism, with 400 factories . suspected of having links with China destroyed or damaged by mobs. One Chinese worker was killed and scores more injured at a huge Taiwanese steel mill that was overrun by a 1,000-strong crowd. 'The . prime minister requests and calls on every Vietnamese to boost their . patriotism to defend the fatherland's sacred sovereignty with actions in . line with the law,' the text message said. 'Bad elements should not be allowed to instigate extremist actions that harm the interests and image of the country.' There were no reports of any new violence or protests on Friday. Firefighters stand across from the main entrance of Tan Than Industries as the Taiwanese bicycle factory burns, in Di An Town, Binh Duong province, Vietnam . Protesters stand on the corner of a street in Binh Duong province, near Song Than 2 Industrial Park in Vietnam . Vietnam's authoritarian leaders typically clamp down on public protests of any sort, but have allowed them this time. Preventing people from demonstrating would have given fuel to domestic critics of the government who already accuse it of being soft on Beijing. The government is also able to use the nationalist sentiment of its people to amplify its protests to Beijing. But violence that harms foreign investment and risks spinning out of control is unlikely to fit into this strategy, and the government will attempt to ensure that it doesn't break out again, most analysts say. China and Vietnam have tussled for years over competing territorial claims, as have the Philippines and China. But Beijing's desire for oil and gas, and its growing economic and military might, have seen it take an increasingly assertive stance to its claims in the sea, triggering increased tensions and incidents between it and claimant states. The anti-China violence on the streets is only inflaming the relationship further. China said its foreign minister, Wang Yi, called Vietnamese Foreign Minister Pham Binh Minh on Thursday and expressed Beijing's 'strong condemnation and stern protest' over the violence against Chinese and other foreign nationals and businesses. The U.S. doesn't take a side in the disputes, but shares many of the concerns of Vietnam and the Philippines about China. On Tuesday, Kerry said during a phone call with Chinese Foreign Minister Wang Yi that China's introduction of the oil rig and numerous government vessels into the area disputed with Vietnam was 'provocative', a State Department spokeswoman confirmed.
Philippine foreign ministry claims Beijing is building airstrip on disputed reef .
Minister says China has been moving earth and materials onto an island .
Tensions already high after China moved oil rig into area claimed by Vietnam .
Beijing and Hanoi each accused the other of ramming ships in disputed area .
Vietnam's PM texts citizens urging them to defend country's sovereignty .
China has been accused by the Philippines of reclaiming land on a reef in disputed islands to build an airstrip just days after Washington described Beijing's actions in the region as 'provocative'. If confirmed, the airstrip would be the first built by China on any of the eight reefs and islands it occupies in the Spratly Islands in the South China Sea. It would also mark a significant escalation in tensions involving several nations in the area. China claims almost the entire South China Sea, an area rich in energy deposits and an important passageway traversed each year by $5trillion worth of ship-borne goods. Scroll down for video . Outrage: Vietnamese and Filipino protesters outside the Chinese Consulate at the financial district of Makati city to protest the recent moves by China to construct an oil rig in disputed waters in the South China Sea . Location: If confirmed, the airstrip would be the first built by China on any of the eight reefs and islands it occupies in the Spratly Islands in the South China Sea . Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims on the area. Philippine . Foreign ministry spokesman Charles Jose told Reuters that China had . been moving earth and materials to Johnson South Reef, known by the . Chinese as Chigua, in recent weeks. He . said China was reclaiming land in violation of the Declaration on the . Conduct of Parties in the South China Sea, an informal code of conduct . for the region. 'They're about to build an airstrip,' Jose said. He said evidence of the Chinese activity on the reef had been shown in aerial photographs taken by the Philippine Navy. Tensions rise: Chinese coast guard vessels (right) and an unidentified naval vessel (left) near China's oil drilling rig (centre) in disputed waters in the South China Sea, off the coast of Vietnam . On patrol: Chinese coast guard vessels in the South China Sea. Beijing and Hanoi each accused the other of ramming its ships near the disputed Paracel Islands where China has moved a large oil rig . The Philippines and Taiwan already have airstrips in the area. The . ministry had already lodged a protest with the Chinese and raised the . issue behind closed doors at last weekend's summit of the Association of . South East Asian Nations in Myanmar, Jose said. Tensions in the South China Sea were already high after China moved a large oil rig into an area also claimed by Vietnam. Beijing and Hanoi each accused the other of ramming its ships near the disputed Paracel Islands. It . came as Vietnam's prime minister sent a text message to millions of . citizens urging them to act in defense of the country's sovereignty . following China's deployment of the oil rig, but said that 'bad . elements' shouldn't be allowed to engage in violence. The . message, sent late Thursday and Friday to subscribers via major . state-owned cellphone operators, didn't directly condemn the riots that . have broken out this week following China's decision to deploy the rig . off the coast of central Vietnam on May 1. Vietnam's prime minister sent a text message to millions of citizens urging them to act in defense of the country's sovereignty following China's deployment of the oil rig . On the lookout: A Vietnamese coast guard officer watches one of his vessels vessel in the South China Sea . Vietnamese patrol ships sent to disrupt the rig are currently locked in a tense standoff with Chinese ships guarding it. Anti-China protests that started . peacefully have ended in violence and vandalism, with 400 factories . suspected of having links with China destroyed or damaged by mobs. One Chinese worker was killed and scores more injured at a huge Taiwanese steel mill that was overrun by a 1,000-strong crowd. 'The . prime minister requests and calls on every Vietnamese to boost their . patriotism to defend the fatherland's sacred sovereignty with actions in . line with the law,' the text message said. 'Bad elements should not be allowed to instigate extremist actions that harm the interests and image of the country.' There were no reports of any new violence or protests on Friday. Firefighters stand across from the main entrance of Tan Than Industries as the Taiwanese bicycle factory burns, in Di An Town, Binh Duong province, Vietnam . Protesters stand on the corner of a street in Binh Duong province, near Song Than 2 Industrial Park in Vietnam . Vietnam's authoritarian leaders typically clamp down on public protests of any sort, but have allowed them this time. Preventing people from demonstrating would have given fuel to domestic critics of the government who already accuse it of being soft on Beijing. The government is also able to use the nationalist sentiment of its people to amplify its protests to Beijing. But violence that harms foreign investment and risks spinning out of control is unlikely to fit into this strategy, and the government will attempt to ensure that it doesn't break out again, most analysts say. China and Vietnam have tussled for years over competing territorial claims, as have the Philippines and China. But Beijing's desire for oil and gas, and its growing economic and military might, have seen it take an increasingly assertive stance to its claims in the sea, triggering increased tensions and incidents between it and claimant states. The anti-China violence on the streets is only inflaming the relationship further. China said its foreign minister, Wang Yi, called Vietnamese Foreign Minister Pham Binh Minh on Thursday and expressed Beijing's 'strong condemnation and stern protest' over the violence against Chinese and other foreign nationals and businesses. The U.S. doesn't take a side in the disputes, but shares many of the concerns of Vietnam and the Philippines about China. On Tuesday, Kerry said during a phone call with Chinese Foreign Minister Wang Yi that China's introduction of the oil rig and numerous government vessels into the area disputed with Vietnam was 'provocative', a State Department spokeswoman confirmed.
China has been accused by the Philippines of on the area. Philippine . Foreign ministry had . been moving earth and materials to Johnson Sea were already high after China moved a large oil rig into an area also claimed by Vietnam. Beijing and Hanoi each accused the other of to millions of citizens urging them to act in defense of the country's sovereignty following