Several people have died and scores are injured after a train hit a car on a level crossing in Berkshire.
At least eight carriages are thought to have been derailed and six people may still be trapped inside the wreckage.
The train, the 1735 First Great Western service from London Paddington to Plymouth, was derailed near Ufton Nervet, between Newbury and Reading.
There were around 150 casualties in the crash of whom several were dead, ambulance service officials said.
The train was derailed at around 1815 GMT.
Police are checking fields surrounding the crash site for any walking wounded.
Casualties have been taken to the Royal Berkshire Hospital in Reading and the North Hampshire Hospital in Basingstoke.
The train hit a car at an unmanned level crossing around 500m from the A4.
We came to a juddering halt and suddenly the lights went off, screaming, shouting and it went pitch black
BBC Radio Five Live
'There was total chaos'
The Royal Berkshire hospital says it has received one coachload of walking wounded.
Passenger Mario Iotti told BBC News: "I heard the noise of the wheels screeching very loud. There was broken glass all over the track.
"The whole thing tilted to the left side of the tracks. My carriage remained on the tracks but on its side, sliding along.
"I could see some people at the side of the tracks. I saw one carriage smashed in completely. It was a big pile of wreckage.
"As far as I can recall some people were struggling, with broken legs and arms, but 95% were without major injuries, which is great.
"It is unbelievable to think you could go through that kind of thing and even survive."
One of the train's passengers, Jonny Saunders, who works for BBC Radio Five Live, said he and his fellow passengers were "in complete shock".
He said: "There was suddenly this extraordinary stopping sensation, as if someone had pulled the emergency cord, but it carried on and carried on.
"We came to a juddering halt and suddenly the lights went off, screaming, shouting and it went pitch black, then total chaos in the carriage for a few moments.
"I was incredibly lucky because the carriage I was in didn't actually go over on its side, but the carriage in front of me did go over on its side and the carriage behind me went over on its side."
He said passengers were being treated in a local pub by paramedics.
Tim Grundy, an eyewitness to the aftermath, said the train look like a "twisted baguette".
He said the middle sections were completely destroyed.
Our particular carriage went on to its side, about a 45 degree angle
He said: "There seem to be hundreds of people running up and down the train line.
"I have never seen so many ambulances in my life. I suspect there may be quite a few people hurt here."
Emergency services had set up arc lights and firefighters were using cutting equipment to rescue trapped passengers.
Richard Micklewright, who was on the train, said it looked like carriages were "strewn all over the place".
He said: "Our particular carriage went on to its side, about a 45 degree angle but fortunately it stopped shortly after that.
"I can tell you the carriage in front of us was upright, the one before that ended up at a right-angle to the tracks, beyond that I couldn't see clearly."
He also praised the emergency services, saying they had arrived in around 10 or 15 minutes.
Emergency services were at the scene 'within minutes'
A spokesman for Berkshire Fire Service said 10 fire engines at the scene have been using special cutting equipment to free people.
He said: "We are using similar equipment to what we would use to free people from cars, but we have had to upgrade it because trains have more reinforcement."
Keith Lumley, a Network Rail spokesman, said the accident happened at an automatic level crossing with half barriers on each side of the road.
First Great Western has warned of severe travel disruption due to the closed line.
People worried about friends or relatives who may have been on the train are asked to call 08458 505505. The Thames Valley Police casualty bureau number is 0870 010 0732.