The prisoners were "taken out" of the vehicle by a number of "armed masked men", Greater Manchester Police said.
Officers were called to Trinity Way following reports that a jail van had been attacked shortly before 8.30am.
The gang made off in a Saab, which was found abandoned in Barrow Street, Salford, a short time later.
A security guard was taken to hospital, but his injuries are not believed to be life-threatening.
Police have cordoned off a bridge in Trinity Way, where a white Leyland DAF G4S security van remained with its driver's side door open.
It is believed the vehicle was taking the inmates to Salford Magistrates Court from Strangeways Prison, although this has not yet been confirmed.
Detective Sergeant Paul Copplestone said: "We are sure that this incident was witnessed by many people at a very busy time of the morning.
"The Saab was driven off towards the M602 motorway.
"We would urge witnesses to contact us."
:: Anyone with information is asked to call police on 0161 872 5050 or they can call Crimestoppers anonymously on 0800 555 111 .
Souce: Yahoo new.
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