Daylight on Wednesday revealed the destruction and devastation caused by an Amtrak train derailment in Philadelphia that left at least six people dead and injured dozens more, six critically. Some survivors had to scramble through the windows of toppled cars to escape. One of the seven cars was completely mangled. The accident has closed the nation's busiest rail corridor between New York and Washington as federal investigators begin sifting through the twisted remains to determine what went wrong. Train 188, a Northeast Regional, left Washington, D.C. and was headed to New York when it derailed shortly after 9 p.m. Tuesday. Amtrak said the train was carrying 238 passengers and five crew members. Mayor Michael Nutter, who confirmed the deaths, said the scene was horrific and not all the people on the train had been accounted for. 'It is an absolute disastrous mess,' he said. 'I've never seen anything like this in my life.' He said all seven train cars, including the engine, were in 'various stages of disarray.' He said there were cars that were 'completely overturned, on their side, ripped apart.' More than 140 people went to hospitals to be evaluated or treated. Amtrak said the cause of the derailment was not known and that it was investigating. The National Transportation Safety Board and the Federal Railroad Administration were also dispatching investigators to the site. Early Wednesday morning, authorities on the scene seemed to be girding for a long haul. One sign: several portable toilets were delivered for investigators and recovery workers. Utility poles near the wreck could be seen leaning into the tracks.