At least six people were killed late Tuesday when an Amtrak train derailed outside Philadelphia.

According to Fox News, emergency officials confirmed that six other people were critically injured and more than 140 others were transported to local hospitals for evaluation or treatment. Philadelphia Mayor Michael Nutter told reporters this morning that not all of the passengers on the train's manifest had been accounted for.

There's no word yet on a potential cause of the crash.

Amtrak has released a statement saying it was "deeply saddened by the loss of life". The company earlier announced that people seeking information about friends or relatives on the train could call a special hotline at 1-800-523-9101.

Here are some pictures and videos from the scene:

Here, witnesses describe the moment of impact when the train crashed: