Washington  - Two subway trains collided Monday in the US capital Washington, leaving four people dead and scores injured, Mayor Adrian Fenty said.

The accident occurred around 5 pm (2100 GMT) near Washington's border with the state of Maryland, on a section of track above ground.

One train had apparently stopped between stations before being struck from behind by a second train.

Local news footage showed one heavily damaged carriage pushed up on top of another. The force of the collision tore the floor out of the moving train as it vaulted onto the stopped carriage.

The driver of the moving train was reported among the dead.

Washington Fire Chief Dennis Rubin said that the 66 injured included 50 "walking wounded." Twelve people suffered serious injuries, two were in critical condition, and two others were airlifted to a hospital.

A reporter for local broadcaster ABC 7 described seeing several people with broken bones.

John Catoe, chief of the multi-jurisdictional agency that runs the Metro train and bus system through Washington and the adjoining suburbs in Maryland and Virginia, said that firefighters were still searching the wreckage for any additional victims.

Washington Fire Department spokesman Allan Etter said that rescue workers were engaged in "mass-casualty operations."

The transit authority, bracing for substantial delays around the region, recommended that commuters who regularly used the affected train lines use different routes or other modes of transportation.

The accident is the deadliest in the 33-year history of Washington's subway system. (dpa)