MARAWI CITY, Philippines (Reuters) - War might still be raging in the ruins of the Philippine city of Marawi, but the cleanup has already began.  Under the guard of dozens of police and soldiers, about 100 of the 200,000 residents driven from their homes during 150 days of fighting have returned to start what will be a massive operation to clear the city of the debris of war. Army trucks crawled through the deserted streets to take displaced people to safe areas of Marawi, where echoes of gunfire and explosions could still be heard as troops sought to finish off the remaining Maute group militants hemmed into a shrinking battle zone. They swept away trash, rocks and belongings scattered on streets, among them toys of children who fled when the pro-Islamic State rebels ran amok on May 23, setting buildings ablaze and ransacking churches and schools. Spray painted on the shutter of one abandoned building reads  Maute ISIS , a term used for the militant alliance.  This is very important for the normalization of Marawi because we are responding to the call for them to return back, so we need to prepare,  said Lieutenant Colonel Rosendo Abad of a joint task force. Defense officials say it could take until January before rebuilding can start, with the heart of the city littered with unexploded bombs and booby traps and buildings on the brink of collapse after months of government air strikes. Military operations have cost 5 billion pesos ($97 million) and the government estimates it could be 10 times that much to rebuild Marawi. The government on Tuesday said 20-year  patriotic bonds  would be sold to generate 30 billion pesos. Australia, the United States, Singapore, Russia, the World Bank and the Asian Development Bank are among the countries and organizations that have offered to help. But already close to the front lines of the effort is China, which has donated 47 heavy-duty industrial vehicles, among them excavators, bulldozers, tractors, cement mixers and dump trucks.    Those vehicles are on standby at the port in nearby Iligan City, waiting for the guns to finally go silent before starting the task of restoring the country s only designated Islamic City. Omarshariff Yassin, an engineer in charge of equipment at the Department of Public Works and Highways, said there was enough skilled manpower, but a lack of machinery.  Before the Chinese equipment arrived, we have 15 equipment in use. We have 17 units on standby,  he said.  The more, the better. What s happening is we lack equipment so we borrow from other regions. But we really need more.   