Two commuter trains collided in a tunnel outside Caracas, Venezuela, killing one person, injuring about 30 and leaving frightened passengers gasping for air in the dark.
One train suddenly braked due to an apparent malfunction and another crashed into it from the rear, causing the first to derail, transportation minister Francisco Garces said on state television.
Officials said a packed train coming in the opposite direction was able to stop before colliding with the others, averting a possible disaster.
The crash apparently cut power in the tunnel between Caracas and the suburbs of Los Valles del Tuy.
Passengers "remained inside the wagons without air conditioning and within the tunnel", causing some to feel a sense of suffocation, said Victor Lira, civil defence director for Miranda state.
He said five people suffered scrapes or trauma while the other injured were treated for respiratory problems or high blood pressure.
Mr Lira said the engineer of the rear train died.
President Hugo Chavez urged Venezuelans not to speculate about possible causes but to await the results of an investigation.
"I lament the death of an employee, the driver of the train," he said.
The injury toll was low in part because the trains that collided were almost empty, heading out of the capital as rush hour traffic flowed the other way, Mr Lira said. He said one of the trains had about 40 passengers on board, while the other was not carrying any.
The train that managed to avoid the crash was filled with about 1,000 people.
They were among about 3,000 people evacuated from the area, including about 2,000 who were aboard other trains not involved in the accident, officials said.
Rescuers drove trucks over the tracks into the tunnel to evacuate some of the passengers. Hundreds walked out of the tunnel on foot, and others rode on small maintenance trains.
About 100 people, most of them elderly people and children, were evacuated by helicopter.
The government sent buses to carry passengers whose trains were blocked by the crash, adding to the normally heavy traffic.
The 25-mile train line carries about 60,000 passengers a day.