Crews are continuing to pour through the wreckage¹ of a train derailment in the US city of Philadelphia.

At least 7 people are dead and over 200 others hurt.

Authorities say a number of passengers remain unaccounted for.

Walter Sumwalt with the US National Transportation² Safety Board says they're beginning their probe into exactly what happened.

"We've brought a multi-disciplinary team in here that will be covering a number of issues. We're looking at the track, the train signals, the operation of the train, the mechanical condition of the train, human performance. We're setting up a multi-disciplinary investigation³ to try and understand the factors that led to this accident."

The train was en route from Washington to New York when it jumped tracks on Tuesday night.

So far there's no indication at this point as to what may have led to the derailment.