5 Things to Know About Amtrak Crash

— -- Your look at the key topics surrounding Tuesday's Amtrak train derailment in Philadelphia.

1. Investigators Search for Cause of Train Derailment

Federal investigators will visit the site of an Amtrak crash in northeast Philadelphia this morning, trying to uncover the cause of a train derailment responsible for at least five deaths.

The accident happened at about 9:28 p.m., with six cars overturning and the engine separating from the rest of the train.

2. Numerous Passengers Dead, Injured

In addition to five known casualties, more than 200 people were treated at area hospitals, authorities said.

"It is an absolute disastrous mess," Philadelphia Mayor Michael Nutter said at a press conference. "Never seen anything like this in my life."

3. Tense Moments Follow Crash

Dozens of the 238 passengers on board the New York City-bound Amtrak train had to make their way through the flipped cars to get to safety.

Video shot by one of the passengers, Philadelphia-based MC Yameen Allworld, shows the darkness and confusion that faced survivors as they tried to crawl out of the wreck.

"Crawl forward, sir," he is heard saying in a video that he posted on Instagram.

4. Travel Concerns

Amtrak service between New York and Philadelphia remains shut down today.

5. Site of Train Derailment Isn't New to Railway Tragedy

On Sept. 6, 1943, a Pennsylvania Railroad train crashed at Frankford Junction in northeast Philadelphia, killing 79 people and injuring 117 others.

The 541 passengers on board the Congressional Limited train that day had been traveling for Labor Day weekend. Service members were on board.