A manhunt is under way for two murderers who pulled off an elaborate overnight escape from a New York state maximum security prison.
Prison guards discovered that the men were missing during an early morning bed check in the Clinton Correctional Facility, in Dannemora, about 65km south of the Canadian province of Quebec. Both inmates are considered a danger to the public, state police said.
New York Governor Andrew Cuomo said the escape - the first from the prison's maximum security facility in its 150-year history - was "sophisticated".
The two men were in adjoining cells and cut a hole through the back wall, crawling through the opening overnight, a prison official said.
They scaled a catwalk, then used power tools to drill through metal walls and a steam pipe, finally weaving through interior tunnels and coming out through a manhole cover on the street, Cuomo said.
The men had left items in their beds, like clothing, to make it appear they were asleep, he said. It was not yet known how they obtained power tools or figured out how to make their way through the tunnels to the street.
The breakout was reminiscent of the one depicted in The Shawshank Redemption, the 1994 film based on a Stephen King story.
"You look at the precision of the operation. It was truly extraordinary," Cuomo said at a press conference outside the prison, known as "Little Siberia" for its remote location 515 miles north of New York City and the region's cold climate.
About 200 law enforcement officers were searching the area around Dannemora using dogs and backed by police helicopters, authorities said. Police were asking people to be on the lookout and alert authorities if they saw the two men. Cuomo stressed that no one should approach them. "These are not people to be trifled with."
The convicts were identified as Richard Matt (48), serving 25 years to life for three counts of murder, kidnapping and robbery.
The other prisoner, David Sweat (34), is serving a life sentence without the possibility of parole for the murder of a sheriff's deputy.