An inquiry has been launched after a woman's head was trapped between the sliding doors of a moving train.

Passenger watchdog Brighton Line Commuters (BLC) said the victim, referred to as Miss H, was travelling on a Thameslink train between London Bridge and Hassocks on a Friday evening.

The train had pulled into Wivelsfield station, near Burgess Hill, even though it was not scheduled to stop there.

It stood for five minutes with the carriage doors closed but with the "doors open" light on.

Miss H said she opened the doors to see what was going on and to ask someone when the train might be under way again.

Miss H said the doors closed suddenly without the usual warning bleeps.

T3zhe train started to move and the passenger had to struggle for several seconds to wrench her head free.

She was left with rubber marks on her face and pain in both ears.

Miss H's parents made immediate contact with Thameslink to warn them about the train but their call was routed to Newcastle, sparking fears the faulty carriage was still in service.

BLC is now championing the case.

Spokesman Shelley Atlas said: "Miss H's mother was not one of our members but she got in contact with us after it happened. She wrote in with the details and then we got in contact with the company to find out how this happened.

"This must have been a very frightening incident and work needs to be done to make sure it does not happen again.

"Luckily she was not badly hurt but things could have been a lot worse.

"As an organisation we are constantly campaigning for slide-door trains to be introduced, as we strongly believe they are much safer than slam doors.

"But this shows there are also potential safety problems with slide-door trains and people must be aware.

"It was a strange thing to happen as the doors are normally very safe but it shows what can happen."

A spokesman for Thameslink said they were treating the incident very seriously and had launched an investigation.