The manhunt for two inmates who escaped from a New York maximum security prison expanded to neighboring Vermont on Wednesday as the pair set a record for the longest jailbreak in New York history, authorities said.

Richard Matt, 48, and David Sweat, 34, escaped from Clinton Correctional Facility in Dannemora, New York, five days ago, cutting through steel walls, squeezing through a steam pipe and popping out of a manhole.

More than 450 state, federal and local law enforcement agents were searching the area north of New York's rugged Adirondack Park on Wednesday, with the search extending into neighboring Vermont, New York State Police Superintendent Joseph D'Amico told reporters.

They may have had help from a female prison worker who befriended the inmates, New York State police said on Wednesday.

Prior to escaping, the men discussed heading for Vermont, a rural state with dense forests and seasonal cabins, accessible by a ferry across Lake Champlain, about 40 miles (64 km) south of the prison, police said.

The longest previous escape from a New York prison lasted just three days, according to data from the New York Department of Corrections and Community Supervision. In other New York state prison escapes, freedom lasted less than six hours for 60 per cent of the 30 inmates who succeeded in fleeing in the last decade.

Elaborate escape schemes generally require equally detailed plans for fleeing the area and living life under the radar. That is where most fugitives fall short.

"When you escape, not only do you need the essentials like clothing, food and shelter, but you need some sort of long-term plan where your identity will be hidden," said researcher Bryce Peterson, who focuses on inmates and prisons for the Urban Institute's Justice Policy Center.

International publicity surrounding the upstate New York prison break, including photographs and physical descriptions of the tattooed men, make it extremely difficult for them to remain in the shadows, he said.

"The only way you could do that successfully is having people on the outside who will help you," Peterson said. "But the more people you associate with on the outside, the more likely you are to get caught."

FEWER ESCAPES

Matt, who has a history of escape attempts from other lockups, was serving a sentence of 25 years to life. Sweat was serving a life sentence.

Once caught, the convicted murderers will each face a criminal charge of escape, which can carry a seven-year prison term, Horn said.

"Seven more years means nothing to a lifer," Horn said.

While there are newer, more secure prisons in New York, he said, authorities faced with holding inmates who have already escaped one of the nation's most impregnable facilities might consider the controversial policy of solitary confinement.

Nationwide, the number of prison escapes has dropped sharply, from 100 inmates per 10,000 in the 1980s to one per 10,000 today, Peterson said.

He cited several reasons for the drop, including fewer furloughs that present less opportunity to flee, more secure housing and more effective technologies for detecting escape, like motion sensors and surveillance systems. – Reuters