As many as 1.5 million innocent people died at Auschwitz in horrifying conditions: its name a reminder of the atrocities of the Holocaust. But authorities say that the former concentration camp, now the Auschwitz-Birkenau State Museum, in Oświęcim, Poland, is becoming a popular tourist destination - so popular in fact, that they may have to start turning people away. The memorial site today urged potential visitors to book their visits online ahead of time to prevent that from happening. Scroll down for video . A sign in front of a watchtower at Auschwitz I concentration camp, which has become an unlikely tourist . It said there have been more than 250,000 visitors so far this year, a rise of more than 40 per cent compared with the same period last year, which itself hit a record with 1.5 million visitors. 'Going through the Auschwitz-Birkenau space is not an easy experience for anyone,' said Dr. Piotr M.A. Cywiński, Director of the Museum. 'This authentic place has become the symbol of evil for the entire world, which is manifested by an over threefold increase in attendance, interest of the media, internet statistics as well as over half a billion people throughout the planet who watched the 70th anniversary of the liberation of KL Auschwitz live on television.' Tourists take photographs at Auschwitz, which has had more than 250,000 already this year . The memorial site has urged potential visitors to book their visits online ahead of time to ensure entry . The increase in popularity has led to various security changes, and visitors are now advised to book ahead inorder to avoid congestion inside the former Nazi concentration camp. Just 30 people are allowed to visit Auschwitz I - the original camp at any one time - for safety reasons, as well to conserve the buildings and create the best conditions for learning about its history. So a website for the site has been created enabling booking, which  guarantees entrance to the Museum on a chosen day and hour. The site attracted headlines in 2014 when an Alabama teenager took a  selfie during a tour of the death camp . 1. Ground zero – site of 9/11 in New York . 2. Auschwitz – concentration camp, Poland . 3. Alcatraz – prison, San Francisco . 4. Pompeii – Italy . 5. Omaha and Utah beaches – D-Day invasion scenes, France . 6. Killing fields – Cambodia . 7. New Orleans – Site of Hurricane Katrina disaster, USA . 8. Chernobyl – Nuclear disaster site, Ukraine . 9. Giglio, Italy – scene of the Costa Concordia disaster . 10. Haiti – site of devastating earthquake . According to online travel agency sunshine.co.uk . Visitors also have to undergo safety control: It is forbidden to light candles outside designated areas. or to carry objects which may pose a threat to the life, health and safety. Smoking cigarettes and e-cigarettes is also strictly forbidden and only small bags are allowed into the museum. In 2014, 1,534 000 people visited Auschwitz, the highest number during one year than ever before -  the highest attendance in the history of European memorial sites. January saw the  70th anniversary of the camp's liberation, a possible reason for the surge in interest. Auschwitz after its liberation  in January 1945.  A group of children who survived the camp, pictured . January saw the 70th anniversary of the camp's liberation, a possible reason for the surge in interest . It also attracted headlines in 2014 when an Alabama teenager was criticized for taking a smiling selfie during a tour of the German death camp. Visiting scenes of death and disaster might seem inappropriate to the average holidaymaker, but dark tourism appears to be on the rise. Professor Mark Griffiths of Nottingham Trent University, who has written a blog post on death fascination says there are a number of reasons for our interest in the macabre. 'There's a huge market for witnessing the extremities of human behaviour. By looking at something so extreme it makes us feel better about ourselves,' he told MailOnline Travel.
Over 250 thousand people have visited Nazi concentration camp in 2015 . Visits have increased by 40% since same period of the previous year . January saw 70th anniversary of its liberation and a surge in interest .