A passenger train travelling from London to Eastbourne derailed in southern England on Thursday, with three carriages overturning and 11 people injured, including two who suffered serious injuries, British Transport Police said.

The Southern Rail service was carrying around 150 passengers when it went off the tracks outside Lewes, a tourist town in southern England. Nine people sustained minor injuries in the derailment, police said.

The scale of the accident became clear after the train came to a stop, with one of the carriages flipping onto its side and sliding down an embankment into a field.

Passenger Rob Bradley was travelling on the train with his six-year-old daughter when he said the carriage suddenly began rocking as the train picked up speed.

Bradley told the BBC that the carriage appeared to jump upwards before the brakes were applied. The sudden movement sent passengers and their belongings forward.

He said he initially had no idea how badly the train had been damaged. After it stopped, he turned around and saw that the rear section of the train had been opened up, with smoke and dust filling the carriage.

Bradley then saw another carriage lying on its side after sliding down the embankment.

Bradley said he and his daughter were not injured, but he saw passengers from one of the overturned carriages with blood on their heads and clothes.

Another passenger told him they had been cut after a window shattered during the derailment.

Aerial footage from the scene showed firefighters and paramedics treating passengers in a field beside the train. Several ambulances and three helicopters were also deployed at the site.

British Transport Police said all passengers had been evacuated from the train within around three hours of the derailment.

The cause of the train derailment is currently under investigation.

With AP inputs