WASHINGTON (Reuters) - Two Washington, D.C., subway trains collided during the Monday afternoon rush hour, killing nine people and injuring at least 75, officials said early on Tuesday.
A District of Columbia Fire Department official said the death toll had been raised from 6 late on Monday, but said officials were could prepared to identify any of the deceased.
Mayor Adrian Fenty called the crash the deadliest in the 33-year history of the city's Metro subway system.
Officials said one train hit another train that had stopped at a platform, but the cause of the crash was not immediately clear. At least one car from the trailing train was hurled onto the top of the other in the accident, which occurred on above-ground tracks.
"Metro officials do not know the cause of the ... collision and are not likely to know the cause for several days as the investigation unfolds," the Washington Metropolitan Area Transit Authority said on its Web site.
The crash occurred on the heavily traveled red line about 5 p.m. EDT, between Fort Totten and Takoma stations on the northeastern outskirts of the city near the border with Maryland. Both trains were heading south into the city.
It was the first crash involving a passenger death since 1982, when three people were killed in a derailment. The Metro train system began service in 1976.
"What happened ... (was) one train was stopped waiting to get the order to pass. ... The next train came up behind it and, for reasons that we do not know, collided into the back of that train," John Catoe, general manager of the Washington Metropolitan Area Transit Authority, told reporters.
"We are committed to investigate this accident until we determine why this happened and what must be done to ensure it never happens again," Catoe said in a statement.
The transit authority said one of those killed was a female train operator in the trailing train. The accident trapped passengers in one or more of the subway cars.
One witness described how one train appeared to collide with -- and then run up and over -- the second train.
"It was very mangled, everything is ripped out of there," the woman, who was not identified, told the local ABC television affiliate.
Investigators with the National Transportation Safety Board were at the crash site early on Tuesday collecting evidence.
"They will have to do both an investigation and then a release of the scene for us to clean it up," Fenty told reporters at the scene.
Officials encouraged riders to avoid the red line, which they said would be "severely impacted" by the crash.