Update 11:47 p.m. EDT: At least five people are dead after an Amtrak train derailed Tuesday night near Philadelphia, CNN reported, citing Philadelphia Mayor Michael Nutter.

At least six people have been critically injured while 43 passengers have been transported to hospitals, 6abc, a local news network, reported on its Twitter feed.

The National Transportation Safety Board (NTSB) earlier announced on its Twitter feed that its investigators will reach the site of the derailment on Wednesday morning. NTSB also announced that it would hold a media briefing on the accident in the morning.

"We were rolling along nice and smooth and then all of a sudden we were on our side," Don Kelleher, one of the passengers, told NBC Philadelphia.

The network also reported that the northeast rail corridor -- one of the busiest in the nation -- between New York and Philadelphia has been suspended. Local commuter train operators SEPTA and Trenton Regional Rail also suspended some routes after the accident, the report added.

Update 10: 30 p.m. EDT: Amtrak issued a statement about the accident approximately 45 minutes after one of the first people tweeted about the incident.

To watch live stream footage of the crash scene, click here to see video provided by WJZY. 

Update 10:03 p.m. EDT: There were approximately 240 people on board when the train crashed. Multiple medical units rushed to the scene, Twitter user David Levenson wrote.

In a statement on their official Twitter account, Amtrak acknowledged the accident: “We are aware of the derailment of Northeast Regional train 188 north of Philadelphia and will provide updates as they become available.” An old, cryptic tweet remained on their official Twitter account from two hours before the crash. “Come experience the magic of train travel with us,” the tweet said. “Why traveling by train to DC is the only way to go,” a message from earlier in the day said. 

Overhead pictures of the accident posted by CBS Philly showed the train was entirely off the tracks.

The National Transportation Safety Board issued a tweet that said they were “currently gathering information about tonight’s Amtrak derailment in Philadelphia.”

First responders asked for news helicopters to flash their lights on the accident, ABC 2 news reporter Jamie Costello tweeted. Passenger Beth Davidz shared a picture of the scene that showed how dark it was.

Original story: An Amtrak train derailed at Frankford Avenue and Wheatsheaf Lane near Philadelphia Tuesday, WPVI reporter Jim Gardener tweeted. More than 50 people were injured, though the extent of the injuries were unclear.

Former Pennsylvania Congressman Patrick Murphy, the first Iraq war veteran to be elected to Congress, was one of the first people to post photos of the accident to Twitter. His first message, a photo that showed the train car on its side with bloody passengers, was quickly shared hundreds of times .

Murphy followed up that post with a tweet that said he was on an Amtrack train that crashed and that he was helping injured people.

A third follow-up was a photo of a firefighter inside the train. No one appeared to be hurt in that image.

This is a developing story…