12/02/2013 07:00 EST | Updated 02/01/2014 05:59 EST

NYC's Metro North train derailment cleanup underway

The engine of a commuter train that derailed in New York City on Sunday morning, killing four people, is upright again, railway officials say.

Metro-North spokesman Aaron Donovan told The Associated Press that cranes re-railed the engine at 4:20 a.m. ET Monday.

Two cranes are in place to lift the rest of the derailed cars, pending approval from the U.S. National Transportation and Safety Board. Federal investigators are at the site, CBS News reporter Marlie Hall told CBC News Network from the scene Monday morning.

"They are poring over the wreckage, trying to determine what led to that deadly derailment," she said, adding that some issues they'll be looking at are:

- The train's speed at the time of the crash.

- Whether mechanical failure played a role.

- If there any operational errors.

Donovan said about 150 people were aboard when the train derailed as it rounded a riverside curve in the Bronx. More than 60 people were injured. All passengers have been accounted for.

The accident occurred on the Hudson line, which carries 26,000 weekday riders. The commute was expected to be slower Monday morning.

"Train officials are making shuttle buses available to commuters," Hall said. "But they are encouraging anyone that can telecommute to work from home."