Nine people are believed to have been killed after two Washington Metro trains collided in rush hour.

The crash, which took place last night and ended with a large section of one train sitting on top of the other, occurred in northeast Washington, just near the border with Maryland.

The Metro confirmed that one of those killed was a train driver.

Washington fire officials reported that more than 76 people were injured, including two who were in a critical condition. At least 30 people were taken to area hospitals while others suffered minor bumps and scrapes as a result of the impact. Two of the more than 200 firefighters on the scene were among the injured.

Rescuers had to cut open the passenger cars to reach the injured. Local television showed people being removed from the tracks on stretchers.

John Catoe, the Metro general manager, who was on the scene shortly after the accident, was unbale to explain how the crash happened.

Later reports indicated that the trains were travelling in the same direction, with one running into the other from behind. The woman driver of the second train is reportedly the operator who was killed.

Last month, the Washington Metro rail system averaged nearly 300,000 passengers a day. The Red Line, on which the accident happened, is by far the busiest of the system’s six routes, accounting for more than half of its passengers.

The 33-year-old system has suffered severa; previous collisions, the last of which was also on the Red Line, in 2004. In that accident no one was killed but 20 people were injured.

Unconfirmed passenger reports from the scene suggested that Metro may have been conducting track maintenance earlier in the day, which might have contributed to the accident. During repairs, trains often share tracks, though speeds are usually slowed significantly.

The National Transportation Safety Board was on the scene within hours of the accident to investigate the cause of the crash. The FBI was also present, though it was quick to point out that nothing yet suggested that anything criminal was involved in the incident.

The last serious transit accident in the US occurred last September in Los Angeles, when a commuter train operator was sending text messages while driving. That crash killed 25 and injured 134 more.

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