Firefighters and police on Sunday searched the wreckage of a train crash that killed six people and seriously injured 11 others when a train struck a car stopped on the tracks at a crossing.

The locomotive struck the car and derailed at about 6:30 p.m. Saturday, killing the train driver, the person in the car and four train passengers, Thames Valley (search) Police said.

An off-duty police officer who happened to be in the area saw the car drive onto the crossing and remain there as automatic barriers blocking one lane on each side of the tracks fell, said Andy Trotter, Deputy Chief Constable of the British Transport Police.

The officer called for the emergency services after seeing the train hit the vehicle. Trotter gave no details about why the car was believed to have stopped on the crossing.

More than 20 ambulances and 14 fire engines rushed to the scene at Ufton Nervet near Reading, 36 miles west of London. Emergency workers had freed passengers trapped in the wreckage by 11:30 p.m. Saturday, said the fire service.

But firefighters and police with dogs searched the area and surrounding fields until first light to ensure there were no other casualties lying nearby, Trotter said.

Passenger David White, 48, described the crash.

"You could feel it hit the car, breaking hard," he said. "We knew something was happening and the carriages plowed into each other." He said passengers were plunged into complete darkness with people "screaming and shouting on the floor" as tables fell on top of them.

It was the first major accident on Britain's rail network since 2002, when seven people died in a crash at the suburban Potters Bar (search) station north of London. That crash and five other big train accidents killed 59 people over five years from 1997. Several of the crashes were blamed on poorly maintained tracks.

Thames Valley Police said at least eight carriages on the service from London Paddington to Plymouth in southwest England derailed and one was split in two by the force of the impact.

TV pictures Sunday morning showed the derailed train wagons jumbled on the line and what appeared to be a car wheel.

The train was carrying about 300 passengers. Some 80 people were treated at two local hospitals for injuries, although many had only minor cuts and bruises, ambulance and hospital officials said.

"This is clearly a very serious accident and my deepest sympathies are with those involved and affected," Transport Secretary Alastair Darling said.

The intersection where the crash occurred is known as an automatic half-barrier crossing. The half-barriers don't block all of the road, only oncoming traffic in each direction. This allows cars to leave the crossing once the barriers have descended if they have been accidentally caught in-between.