British police are investigating after up to 200 disgruntled passengers halted a train then disembarked and walked down the railway track.
The incident happened in the Redland area of Bristol shortly after the service left Clifton Down railway station at 3.30pm on Saturday.
Passengers had previously been informed that the train would not be stopping at the next station, Redland, as it was too busy.
A group of rail users halted the train by pulling on the emergency cord, then got off and began to walk back towards the station.
Officers from British Transport Police (BTP), who are treating the incident as trespass, helped move the group off the line and to safety.
A spokeswoman for the force said initial reports suggested 80 people were walking on the line but officers saw up to 200 on arrival.
“It was established that, as the train came to a stop shortly after leaving Clifton railway station, the emergency cord had been pulled and people had got off the train and started to walk back towards the station,” she said.
“BTP officers at the scene helped to get the group off the line and to a place of safety.
“We are treating this as a trespass incident – one which caused numerous delays to services in the area and could have put lives in danger – and inquiries are currently under way to identify those involved.”
West Country Travel tweeted an image of crowds on the line, captioned: “This is why trains were cancelled between Severn Beach & Bristol yesterday, because of students on the line at Redland.”
Julian Burnell, of Network Rail, said the actions of the passengers had endangered themselves and other train users.
“Railway lines are designed for trains, not people and are inherently dangerous places,” he said.
“The actions of this group of passengers, whatever their reasons, endangered not only themselves, but also their fellow passengers. We will be investigating.”
A spokesman for Great Western Railway added: “These individuals put themselves and others at great risk, and inconvenienced hundreds of other people.
“The railway is a hazardous environment, which is why railway trespass is a criminal offence, carrying a maximum fine of £1000.
“We will be assisting BTP in their inquiries.”