LONDON (AP) _ A helicopter reportedly hijacked at gunpoint landed on a field inside a maximum-security prison, and two convicts who were exercising nearby jumped aboard and flew to freedom.

The prisoners, who were described as armed and dangerous, were serving time at Gartree Prison in Leicestershire for murder and burglary.

News reports said other inmates stopped prison guards who were trying to reach the escapees as they ran across the exercise yard for the helicopter.

The helicopter apparently had been chartered at Stanstead Airport, north of London, to fly over a golf course, but the reports said the pilot was forced at gunpoint to fly to the prison.

The British Broadcasting Corp. said the helicopter, which was on the ground inside the prison for about 30 seconds, later landed at nearby Market Harborough, about 70 miles northwest of London.

There, the BBC said, the men hijacked a van and then a small car. It said police were using helicopters to try to catch the fleeing prisoners.

It was believed to be the first time a helicopter was used in a prison escape in Britain.

The men were identified by the Home Office as Sydney Draper, 39, serving life for murder and theft, and John Kendall, 36, serving eight years for burglary.

Draper was sentenced April 10, 1974. He was one of six men jailed for life for the murder of James Kennedy, a gateman at a British Rail engineering depot in Glasgow during a payroll robbery in December 1973.