Watch the report from ITV Meridian's Derek Johnson
Emergency services have worked through the night at the scene of a train crash in Salisbury, which saw 13 people taken to hospital.
The incident took place in Fisherton Tunnel, when the 1708 Great Western Railway (GWR) service to Bristol Temple Meads partially derailed and damaged signalling in the area.
The 1720 South Western Railway (SWR) service to Honiton then crashed into the GWR service, which is believed to have knocked one of the trains onto its side.
It's thought the derailment occurred when the GWR service collided with an object in the tunnel.
The line between Salisbury and Basingstoke is expected to remain closed until at least Thursday, as Network Rail warns the disruption could be felt for 'several days.'
WATCH: Investigations continued throughout the night.
Claire Mann, managing director of South Western Railway, said it is "too early to speculate" about a collision between two trains in a tunnel near Salisbury.
She told Good Morning Britain: "Our focus at the moment is with the customers and colleagues that have been affected by this and obviously working with the emergency services to understand exactly what happened.
"Speculation is really not appropriate at this time. We really need to wait for the investigation to take its course and then we'll know exactly what happened.
"But I would like to say a big thank you to the emergency services who were really swift in response last night, and we moved people from the train quite quickly.
Passenger Angela Mattingly was travelling on one of the trains when they collided:
In response to the Salisbury rail crash, an Office of Rail and Road (ORR) spokesman said: "ORR safety inspectors are on site this morning, working with the Rail Accident Investigation Branch and the British Transport Police to investigate how this incident happened.
"It is too early to speculate on the cause, and our investigation will work to understand the full circumstances.
"Our thoughts are with all the passengers that were injured."
Three people remain in Salisbury Hospital in a stable condition following the train crash.
A total of 13 people were treated and the hospital have thanked its staff who "responded with both compassion and care."
Salisbury NHS Foundation Trust said on Monday morning four injured in the crash were admitted to hospital and one patient was discharged.
“We are pleased to report that all are in a stable condition,” the trust added.
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.
Claire Mann, Managing Director, SWR:
"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."
WATCH: Dorset and Wiltshire Fire and Rescue issued this statement at a press conference.
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."
WATCH: St Marks Church took in members of the public who were on board the trains when the incident occured.
Rev Andy Bousfield opened St Marks Church when he heard about the incident, saying the response from the local community was brilliant.
He said if the "church isn't available during a time of crisis, what is it here for?".
Locals donated blankets, tea and coffee, as well as their own free time to come and support those involved in the incident.
Rev Bousfield added that "many people just wanted a chat and a cup of tea".
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."
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.