A major rail accident investigation is underway following a collision between two trains in Salisbury.

The incident happened when a carriage was derailed after hitting an object and a second train then crashed into it when signalling was damaged.

British Transport Police (BTP) said “a number of people” were injured in the incident, which occurred at Fisherton Tunnel.

In a statement late on Sunday night, BTP confirmed there were no fatalities in the incident but a “small number” of people, including the driver of one of the trains, were taken to hospital to have their injuries assessed.

The statement said: “We were called to Fisherton Tunnel in Salisbury at 6.46pm tonight following reports of a train derailment which involved two passenger trains colliding.

“Officers are continuing to respond to the incident alongside our emergency service colleagues and the line is expected to be shut for some time.

“Thankfully there have been no fatalities however a number of people have been injured and a casualty centre has been opened at a nearby church.

“Most of these people are walking wounded however a small number, including the driver, have been taken to hospital where their injuries are being assessed.

“A major incident has been declared and this has been a large scale, multi-agency response working closely alongside our colleagues in Wiltshire. We will remain on scene throughout the night working to establish the full circumstances of how this incident came to happen.”

Dorset & Wiltshire Fire and Rescue Service said in a statement it had helped evacuate “approximately 100 people” from the scene.

The driver had been trapped after the crash but was released from his cab having sustained injuries that were not believed to be serious, sources confirmed to the PA news agency.

A Network Rail spokesperson said: “At around 7pm this evening, the rear carriage of the 1708 Great Western Railway service from Portsmouth Harbour to Bristol Temple Meads derailed after striking an object on its approach to Salisbury station.

“The derailment knocked out all of the signalling in the area. Subsequently, the 1720 South Western Railway service from London Waterloo to Honiton then collided with the Bristol train.”

After the incident unfolded, the derailed train was believed to be on its side, but the South Western Railway (SWR) train was upright.

In a statement, Great Western Railway (GWR) said the railway in the area would remain closed on Monday as “specialist teams continue their investigations”.

It urged customers not to travel on the affected part of the network, adding the closure would affect SWR trains between Exeter and Basingstoke and GWR trains between Westbury and Portsmouth.

Transport Secretary Grant Shapps tweeted: “My thoughts go out to those affected by the serious rail incident near Salisbury.”

He said the Rail Accident Investigation Branch and Office of Rail and Road will investigate, adding: “We need to understand how this happened to prevent in the future.”

A mother who was out trick or treating with her family nearby likened the noise of the crash to “a bomb” and “thunder”.

Tamar Vellacott said she was walking outside with her young children, mother and partner on Jewell Close, Bishopdown, around a kilometre from the scene.

“It was a noise we’ve never heard before … my young ones started panicking thinking it was a bomb and we said maybe a lorry had crashed on the London Road and not to panic,” the 25-year-old told PA.

“There was no screeching like brakes, just a long rumbling sound like thunder hitting the railway line.”

Transport Salaried Staffs Association general secretary Manuel Cortes said the incident was “a very sobering reminder about why safety on our railways is always paramount”.