A manhunt was under way after two prison officers were threatened at gunpoint and forced to release a prisoner on Wednesday.
No one was hurt in the incident which police say took place as they transported Andrew Farndon, 26, for treatment at West Suffolk Hospital in Bury St Edmunds, Suffolk.
A spokesman for Suffolk Police said: "Officers were contacted just after 6.50pm this evening, Wednesday January 25, by staff at the Accident & Emergency (A&E) reception of the West Suffolk Hospital at Hardwick Lane in Bury St Edmunds who reported they could see a man with a gun outside the A&E department.
"They said the man was pointing the weapon at two prison officers.
"Moments later police received a second call from the prison officers, from HMP Highpoint, who said they had a gun pulled on them by a man who had confronted them as they had arrived at A&E with a prisoner who had been stabbed in an incident at the prison."
The prison officers said the prisoner then ran off across the car park with the man carrying the gun.
Farndon is described as white with a shaved head, and was wearing a dark blue baseball cap and a light coloured jumper that was padded on the right side due to his injury. He was a category C prisoner, who was considered unlikely to make a determined escape attempt.
The man with the gun is described as white, in his mid 40s, around 5ft 8ins tall and of stocky build. He possibly had a Scottish accent and was wearing a white top and blue jeans.
It is thought they may have escaped in a dark coloured car.
Police are searching the area and are liaising with other agencies and talking to witnesses.
Members of the public are advised not to approach either of the men but to call officers straight away.
Three masked men ambushed the van, smashing its windows with sledgehammers and punching the driver. The van was taking inmates from the prison near Redditch to Stafford Crown Court on Monday morning.
Justice Secretary Kenneth Clarke has ordered an inquiry into how Anslow, described as "extremely dangerous" by police, was able to escape from the prison van.
Instead of being transferred in a high-security prison service van with a police escort, Anslow was with other inmates in a van run by a private contractor.
An international manhunt has been launched for Anslow with police liaising with other UK forces, the UK Border Agency and foreign authorities. The search extends to all airports and railway stations.
Anslow, also known as Skitz, has strong connections across the country, including London, as well as overseas, police said.
Detectives are continuing to question a man arrested on suspicion of helping Anslow to escape.