At least two people have died and around 60 have been injured after a train on Rome's underground metro system rammed into the back of another at high speed this morning.
The fire brigade said two people, including a 30-year-old woman, were pulled out of the wreckage dead and some passengers were still trapped underground.
The collision occurred at 9.47am local time when one train arriving at the station at high speed crashed into the back of another that was still discharging passengers at the Piazza Vittorio underground station in the city centre.
Unconfirmed early reports said the driver of the second train did not stop at a red light.
A witness said overhead beams of the station collapsed when the train rammed into the rear of the other, which was stationary with its doors still open.
"About one quarter of the first carriage of the train I was on was totally crushed," a man told Sky Italia TV. "All the lights went out. It was frightening."
Witnesses said people spattered with blood were leaving the station while others were still trapped down below. There were also reports that a electrical panel exploded when the trains crashed.
The fire brigade said it was checking to see if any other victims were still trapped in the Piazza Vittorio metro station just south of the main overground rail terminal in the city centre.
Forensic police officers enter a metro station in Rome after the collision today. Photo: Massimo Percossi
Officials at the scene said there was no indication the accident was related to terrorism.
"I was on the train that hit the other train. The other was really close. I was right near the front of the train. This is my favourite seat. I saw everything," said Fabiano DeSantis, a lawyer.
"I clearly saw a red light then luckily I managed to anticipate the situation because I saw the train before us," he told Reuters Television.
The injured, many of them spattered with blood, were taken to six hospitals in or near the city centre.
A witness said overhead beams of the station collapsed and the lights went out.
"People on our train were saying 'this is a terrorist attack' but later it became clear to all of us that it was an accident," one woman told Sky Italia Television.
"About one quarter of the first carriage of the train I was on was totally crushed," another passenger said.
The entire system of Rome metro's Line A was shut down and ground traffic was backed up throughout the city as ambulances took the injured to hospitals.