A concrete mixer lorry crashed off a bridge and onto the roof of a passenger train today injuring at least seven people.

The lorry driver was trapped in the wreckage of his vehicle after the incident involving the 1505 South West Trains Guildford to London Waterloo service near Oxshott.

Surrey Fire and Rescue service said two passengers had suffered injuries which were preventing paramedics taking them to hospital.

A spokeswoman said: "Two people are medically trapped, meaning they need to be stabilised before they can be taken off."

British Transport Police said the lorry driver and one passenger were "more seriously injured".

She added: "The remainder of the passengers remain onboard the train at this time while emergency services attend to the injured."

Four other people among the 40 passengers suffered minor injuries.

The lorry crashed through a brick wall on a bridge above the busy commuter line, landing on the roof of the third carriage from the back of the eight-carriage train near Oxshott station.

One passenger described on Twitter how he narrowly escaped injury.

The man, who was travelling to work and was still on the train, said: "See this sh*t on TV but it's actually happening to me."

He added: "Imagine we was gonna sit on that carriage too. God blessed us survivors today."

The passenger posted a series of pictures showing how the roof of the train completely caved in.

He said the seriously injured passenger had spinal injuries.

Another passenger told Sky News: "The train just stopped, the lights went out and we were escorted to the carriage in front of us.

"We haven't actually been taken off the train yet. We're still in the carriage.

"But what we can see is them trying to get the lorry driver out and the dent in the carriage which the lorry collapsed on."

Asked what happened first, he said: "All the lights went out and we didn't actually know what happened.

"We thought we'd gone into the carriage in front of us, and then we saw that the lorry had gone on to the carriage.

"Everyone kept pretty calm actually. The train wasn't really full.

"I think there were only two or three people in that carriage."

He added that emergency personnel had boarded the train and handed out bottles of water.

Network Rail said the incident happened at around 1530.

A spokesman said the incident had taken place on a branch line and would therefore not result in major disruption to the network.

Footage broadcast from a helicopter hovering over the incident showed a Premix lorry on the tracks beneath a road bridge.

The train could be seen about 50 metres further up the track away from the lorry.

It appeared that the lorry struck the carriage, caving in part of the roof, before crashing onto the side of the track. None of the carriages were knocked over.

Dozens of emergency services personnel, including firefighters and paramedics, were at the scene and the surrounding area was cordoned off.

The lorry left the road at Warren Lane, a short distance from Oxshott railway station.

A South West Trains spokesman said: "Safety is our absolute priority and we will do everything in our power to assist the investigation into the accident."

A spokesman for the Rail Accident Investigation Branch (RAIB), who examine rail crashes, said: "We are deploying a team to begin an investigation."

A police roadblock was in place tonight to stop traffic going into Oxshott.

Ali Azigaran, a taxi driver who has lived in the area for 30 years, said that the accident came as no surprise.

"It's a dangerous area and a really tricky bridge to cross," he said.

"You go round a corner and then there's a steep downhill bit on to the bridge - if you don't know the area I can see how you could just fall off.

"The poor man must have lost control. It's such a narrow bridge - I can see how it must have happened.

"They need to put in some traffic signals and do something about safety on the bridge. Maybe this will make the council improve the road."

He added: "It's chaos here tonight - they're not even letting residents into Oxshott and people who live there are starting to get angry.

"The traffic is terrible - you can't get within miles of the centre.

"I've heard that they're taking injured people away from the scene and that's why we're being kept out."