Richard Matt, 48, and David Sweat, 34
Police are hunting for Richard Matt, 48, and David Sweat, 34, who broke out of a maximum security prison in New York State.Handout

The half-brother of one of the murderers who escaped from a high-security New York prison has said the escaped convict would rather die than face spending the rest of his life behind bars.

Richard Matt, 48, and David Sweat, 34, escaped from the Clinton Correctional Facility in Dannemora, 20 miles (32km) from the Canadian border on 6 June, after drilling through the steel walls of the prison.

Matt, was serving 25 years to life for three counts of murder, kidnapping and robbery for the torture and dismemberment of his former boss in 1997. Sweat was serving a life sentence without the possibility of parole for the murder of a sheriff's deputy in 2002.

Wayne Schimpf, who testified against Matt during his trial for the murder of businessman William Rickerson, said he was a "thief" and "conman" who had no intention of serving his full sentence.

In a phone interview with Fox News' On The Record, Mr Schimpf said: "He said to me once before that he could do another seven years. There is no way he would do life, ever. I believe they will not take him alive."

Matt had made three earlier attempts to break out of prison, and was successful on an earlier occasion. In 1986, he escaped from New York's Erie County Correctional Facility after scaling a fence and gate topped with razor wire. He went on the run for five days before he was recaptured at a family apartment in Tonawanda.

Mr Schimpf added that Matt could charm any woman he meets to help him make his escape.

"When he took off for Mexico, when he stole my van, he had under $200 in his pocket. Made it down to Texas, crossed the Rio Grande into Mexico. So, this couple of days, I think, is nothing for him. I mean, he has a way of doing it. He is a thief, a conman. Any woman that comes across him, he will try to charm them and he can do it."

Earlier, New York State Police confirmed that a female prison worker was being questioned as a possible accomplice. State Police Superintendent Joseph D'Amico said Joyce Mitchell, an industrial training supervisor at the prison who worked with Sweat and Matt tailoring clothing, is said to have befriended the inmates, and "may have had some role in assisting them."

A huge road and air police search has been mounted to track down the two convicts who have been described as "dangerous". Police have closed a stretch of highway as the search is extended to other areas in New York and Vermont, after it was revealed the men had discussed heading for Vermont before their escape.

More than 450 state, federal and local law enforcement agents have also been searching the area north of New York's Adriondack Park.

There have been sightings of the men with a member of the public reporting seeing two men walking down the street in the town of Wilsboro, acting suspiciously. Police are also questioning a cab driver in Philadelphia who had reported picking up two men matching the killers' descriptions at the city's Amtrak station.

The two escapees, who have been missing for five days, have now set a record for the longest jailbreak in New York history.