The two convicted murderers who escaped a New York maximum security prison near the Canadian border had to have been overheard by someone while they were planning the “elaborate” plot, Gov. Andrew Cuomo said Sunday, as bloodhounds and helicopters were on the hunt for them.

The two murderers who used power tools to escape from prison must have taken days to cut through steel walls and pipes and break through the bricks. 

"It was a sophisticated plan," Cuomo said. "It took a period of time, no doubt, to execute."

New York state is offering a $100,000 reward for information that leads to the capture of the two convicted.

Gov. Andrew Cuomo said Sunday the unusual step is "appropriate" for the situation.

Authorities were investigating how the inmates obtained the power tools they used in the "Shawshank Redemption"-style breakout over the weekend.

David Sweat, 34, was serving a sentence of life without parole for the 2002 killing of a sheriff's deputy. Richard Matt, 48, had been sentenced to 25 years to life for kidnapping, killing and dismembering his former boss in 1997.

"These are killers. They are murderers," the governor said. "There's never been a question about the crimes they committed. They are now on the loose, and our first order of business is apprehending them."

Officials gave no details on how the men managed to avoid detection while cutting their way out. "They had to be heard," Cuomo told ABC's "Good Morning America."

After the search is over, "we'll go through the exact details of what they did and how they did it to ensure this never happens again," Cuomo said later.

Authorities set up roadblocks and brought in bloodhounds and helicopters. Hundreds of law enforcement officers fanned out around the prison, about 20 miles south of the Canadian border, following up on dozens of tips.

"They're going through garages, sheds, homes, stores," said Dannemora local historian Peter Light, who worked at the prison as a correction officer for 31 years and now runs the prison museum inside the facility.

But authorities acknowledged they did not have a good idea where the convicts could be.

Dubbed "Little Siberia" by locals, the prison houses nearly 3,000 inmates, guarded by about 1,400 correction officers. Surrounded by farmland and forests, the prison is only about a 45-minute drive by car to Montreal.

Cuomo said the escapees may have crossed into Canada or headed to another state.

"This is a crisis situation for the state," he said. "These are dangerous men capable of committing grave crimes again."

Prison officials found the inmates' beds inside the 150-year-old Clinton Correctional Facility stuffed with clothes on Saturday morning in an apparent attempt to fool guards making their rounds. On a cut steam pipe, the prisoners left a taunting note containing a crude Asian caricature and the words "Have a nice day."

Officials said the inmates cut through the steel wall at the back of their cell, crawled down a catwalk, broke through a brick wall, cut their way into and out of a steam pipe, and then sliced through the chain and lock on a manhole cover outside the prison.

It was the first escape from the maximum-security portion of the prison, which was built in 1865.

The men may have had assistance outside the prison, perhaps meeting up with someone who helped them leave the area, investigators said.

Cuomo said investigators were confident the men obtained the tools inside the prison. Acting Corrections Commissioner Anthony Annucci said an inventory of prison tools had so far shown none missing and he was in contact with contractors who were doing or had done work at the prison.

Steven Tarsia, brother of slain sheriff's Deputy Kevin Tarsia, said that finding out his brother's killer had escaped "turns your world upside-down all over again."

He said that just the other day, he found he couldn't remember the names of the men responsible for his brother's death.

"All of a sudden, I remember them again," he said.

Tarsia said he couldn't imagine how the men could have gotten power tools and escaped without help, but "I don't know why anybody would help them."

Prison escapes "are a relatively rare event," said Martin Horn, former New York City corrections commissioner who is now a professor at the John Jay College of Criminal Justice. "That tells you that a great deal of planning is involved because it's not an easy thing to accomplish."

In 2003, two convicted murderers Timothy Vail and Timothy Morgan escaped from a maximum-security prison in Chemung County. They were caught the next day, hiding in an abandoned mobile home not far from the prison.

A state investigation concluded that "staff complacency" allowed the inmates to smuggle tools from a prison carpentry shop to enable their escape. Two corrections officers and a carpentry shop instructor were disciplined.

The two inmates had spent a month chiseling a hole through the concrete ceiling of their cell with a sledgehammer head and other shop tools and made dummies with papier mache heads sporting their own clipped hair, which they left in their bunks the night of their escape.

"This escape (Saturday) is not a failure of the prison system as such," Horn said. "The prisoners serving life sentences have nothing else to do but dream up an escape plan. What did they have to lose?"

Horn added: "All over the country, prisoners are thinking and scheming every hour. The fact that escapes are as infrequent as they are is really remarkable. The one thing American prisons do very well is to hold on to their prisoners."

Saturday's escape had law enforcement swarming the area around Dannemora in the Adirondacks.

Beth Nichols, an employee of a Dunkin' Donuts across the street from the prison and a few hundred yards from the manhole where authorities said the men emerged, said their escape was "nerve-wracking."

She said one employee had a panic attack Saturday after being told about the prisoner breakout.

"She got really scared and she cried," Nichols said. The employee lives a walk away on the same road, but authorities would not immediately allow her to enter her home; her mother picked her up.

Dannemora covers just over 1 square mile within the northern reaches of the Adirondack Forest Preserve. The stark white perimeter wall of the prison, topped with guard towers, borders a main street in the town's business district.

The Associated Press contributed to this report.