A commuter train derailed during Thursday morning's rush hour, injuring at least four people and tying up rail travel.

The Virginia Railway Express was carrying 400 passengers toward Washington when the engine and the last three cars went off the tracks just north of Quantico, according to a statement on the company Web site.

The cause of the derailment was not immediately known.

Four people were taken to hospitals for treatment of injuries. "I've been told that all are minor," VRE spokesman Mark Roeber said.

Prince William County Police officer John Bogert said a fifth person was taken from the crash in a life-support unit but he couldn't say if the person suffered an injury or had some other medical condition.

Northbound passenger and freight rail service, including and CSX routes, were disrupted by the derailment. CSX owns the line.

Another VRE train edged up to the derailment site to return passengers to Fredericksburg. The line runs from Fredericksburg and Manassas to Washington and carries approximately 16,000 commuters daily, Roeber said.

Personnel from the National Transportation Safety Board, CSX and Amtrak were on the scene.