A prison van containing Dale Cregan – the killer of Police Constables Nicola Hughes and Fiona Bone – was involved in a road collision in the Preston area on the way to court, sources said.
The van was travelling to Preston Crown Court, where Cregan has been on trial.
Four prison officers suffered minor injuries and have been taken to hospital for treatment, while one prisoner was injured, Greater Manchester Police said.
A statement said: “A road traffic collision occurred by the roundabout at the exit of junction 31A of the M6 northbound.
“The collision involved two prison vans on the way to Preston Crown Court as part of a high profile trial.”
Sources said the crash was simply a collision between two prison vans.
It is understood prison vans in convoy have to travel close together so no vehicles can come between them.
During his trial, one-eyed Cregan admitted he murdered four people and attempted to murder three others.
In the second week of the case at Preston he changed his pleas to guilty to killing policewomen Pc Hughes, 23, and Pc Bone, 32, and on Wednesday – in week 17 of the hearing – he admitted to taking the lives of father and son David Short, 46, and Mark Short, 23.
The 29-year-old also changed his pleas to guilty to attempting to murder three other men as he gunned down Mark Short in the Cotton Tree pub in Droylsden, Greater Manchester, last May but remains on trial as he continues to deny one remaining count of attempted murder.
It is understood Cregan is not the injured prisoner.
The collision is the second time in eight days that vans containing Cregan and his co-defendants have been involved in a crash.
Last Thursday evening, as the convoy made its way back from Preston to HMP Manchester, two prison vans and a police car were involved in a shunt.
The collision caused damage to both prison vans and minor damage to the police car.
Four prison officers received minor injuries, as did a number of prisoners who were travelling in the vehicles.