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Authorities said Wednesday that the two killers who busted out of a maximum-security New York prison over the weekend might have headed for Vermont.

Vermont Gov. Peter Shumlin said there was information that the escapees discussed going to "a camp in Vermont" because the law enforcement presence in the state would be "cooler" than in New York. He did not elaborate.

Shumlin advised people to lock their doors and remain vigilant.

"This is no time to panic," he said. "It's a time to be sensible."

On the fifth day of an expanding search, there was still no sign of the killers, Richard Matt and David Sweat, who cut the steel in their cell walls, shimmied through a 2-foot pipe and popped out of a nearby manhole to freedom last weekend. Vermont authorities put out their own wanted poster Wednesday night.

Vermont wanted poster Vermont State Police Intelligence Center

Near the Clinton Correctional Facility, in the New York village of Dannemora, police with assault rifles and dogs went house to house, retracing their steps.

Law enforcement also set up a checkpoints several miles from the facility, checking cars, opening trunks and talking to drivers.

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Asked whether the fugitive pair could be on the lam forever, New York Gov. Andrew Cuomo vowed: "I am confident we will find them. The only question is when."

Photos: An Inside Look at Killers' Escape Route

State police said more than 500 tips had come in.

"We won't stop until we have these convicts captured," said Joseph D'Amico, superintendent of the New York State Police.

Meanwhile, Canadian authorities have expanded their own search, law enforcement sources on both sides of the border told NBC News.

The initial focus for the Canadians was along 100 miles of the border north of the prison, but it has expanded east and west, along Canada's border with New York, Vermont and New Hampshire, the sources said.

That includes border crossings on land and along the St. Lawrence River and the Great Lakes, they said. But so far, it has not included the loading area in Plattsburgh, New York, for the ferry to Burlington, Vermont — the primary travel route. NBC News observed no checkpoint on the New York side for at least 24 hours.

A spokesperson for the Vermont State Police told NBC News that there was concern that residents may not have been paying close attention to the escape in a neighboring state. Officers were imploring residents to report any break-in, theft or suspicious activity.

Investigators said Wednesday that they were still questioning Joyce Mitchell, an industrial instructor in the prison's tailor shop, where the two inmates worked. On the day the killers were reported missing, she checked into a hospital, complaining of a panic attack.

Authorities said Wednesday that she "befriended" the inmates and may have helped them escape.

Mitchell's ex-husband, Tobey Premo, told NBC News on Wednesday: "She could just be some country girl who got sweet-talked by some city guy."

Premo said he and Mitchell divorced 20 years ago, adding: "I don't know her."

Meanwhile, Mitchell's son, Tobey, told NBC News that his mother was "not the kind of person that's going to risk her life or other people's lives to let these guys escape from prison."

Asked whether his mother might have been taken advantage of, he said: "I don't know. I mean, they both are convicted murderers. I mean, you have an inmate that is in prison for life, you really don't have anything to lose.”

On Tuesday, a tip led police to swarm the town of Willsboro, about 50 miles southeast of the prison. They came up empty-handed.