Two passenger trains have collided in the Bedford area, leaving a number of passengers and crew hurt and one person dead.
Emergency crews are on the scene after the crash happened between two East Midlands Railway (EMR) services shortly after 17:00 BST.
Confirming the death shortly before 21:00 BST, British Transport Police said a major incident had been declared, adding a number of people had also been injured.
Transport Secretary Heidi Alexander earlier said she was "deeply concerned" by reports of the crash, and Bedfordshire Fire and Rescue urged people to avoid the location while they worked at the scene.
The collision happened just south of the Elstow interchange between the A421 and the A6.
Aerial footage of the aftermath shows the two damaged EMR trains with most carriages on the tracks but at least one shunted off.
British Transport Police said just before 18:45 BST that it was responding to reports of a collision near Bedford.
Rail service Thameslink reported that lines between Luton and Bedford had been blocked from around 17:30 BST.
A passengeras on board one of the trains, who spoke to the BBC, said the collision happened at 17:12 BST.
Family and friends of passengers have been told not to go the scene by police.
It has been claimed one of the trains hit another that was either stationary or moving slowly in front of it on the same line.
Passenger Peter Knapp said others on his train saw one ahead of them before the crash.
He told BBC News: "I felt like I'd been in a bomb explosion."
Knapp described seeing "bloodied faces", people with what appeared to be broken legs, and "smoke everywhere".
Another passenger told the BBC that people flew out of their seats in the crash, including someone who hit her husband in the face.
"There was a lot of blood. A lot of people had facial injuries," Shola Mene said.
The RMT union said it had received reports that passengers and onboard train staff have sustained what it described as "serious injuries".
The Rail Accident Investigation branch said it was in Bedford trying to find out exactly what had happened.
It said in a statement on X: "A team of RAIB inspectors is on site at the scene of a collision between two trains near Elstow, to start gathering evidence."
East Midlands Railway has confirmed two of its trains were involved in the collision.
A spokesperson said: "The 16:40 EMR train from Corby to London St Pancras has been involved in a collision with 15:50 Nottingham [to] London St Pancras, at Bedford South.
"We are currently on the scene and working with Network Rail to assist the emergency services.
"Further updates will be provided as soon as more information is established."
The train company had earlier posted online that services to and from London St Pancras were suspended for the rest of the day.
British Transport Police initially said it had responded to a collision between two trains in the Bedford area, and urged people not to travel to the scene.
In a later statement, the force said: "We know that a number of people have been injured and one person has very sadly died.
"A major incident has been declared, and officers are continuing to respond at the scene alongside colleagues from Bedfordshire Police and the local Fire and Rescue and Ambulance Services."
Bedfordshire Fire and Rescue Service said: "Crews are currently in attendance at an incident on the railway just south of Bedford.
"Please avoid the area. Thank you for your co-operation."
East of England Ambulance Service said: "We have sent a number of resources, including air ambulance and our Hazardous Area Response Team, to a major incident on the railway south of #Bedford. We encourage people to avoid the area.
"Further updates will be provided in due course. Please only call 999 in an emergency."
Bedford Hospital and Luton and Dunstable University Hospital have asked people to avoid attending their emergency departments "unless they have a genuine medical emergency".
Both hospitals said in separate X posts: "Our hospitals are currently supporting the active incident in relation to the recent train crash in Bedford.
"We ask the public to avoid attending our Emergency Departments unless they have a genuine medical emergency. Please use NHS services appropriately."
Transport Secretary Heidi Alexander said she was worried by reports of the collision.
She said on X: "I'm deeply concerned to hear reports of the collision involving two East Midlands Railway passenger trains.
"I'm grateful to emergency services who are on the scene, attending to those affected.
"We're working quickly with the rail industry and local partners to support passengers."
Bedford and Kempston MP Mohammad Yasin said the "very serious" incident was "really concerning" and told the BBC he believed there was "a number of casualties".
Health Secretary James Murray said: "I am being kept updated on the collision of two trains between Luton and Bedford.
"A number of people have been injured and I thank first responders who are helping those affected."
