Authorities in the state of New York are offering a reward of more than $100,000 for information leading to the arrest of two convicted murderers who escaped from a maximum security prison.
In a breakout likened to the film The Shawshank Redemption, Richard Matt, 48, and David Sweat, 34, used power tools to break out of the Clinton Correctional Facility in Dannemora.
State governor Andrew Cuomo described the escape as a "crisis situation" and the pair as "dangerous men capable of committing grave crimes again".
Authorities said Matt and Sweat, who left a note for their jailers saying "Have a Nice Day", could have had help.
Despite a huge operation involving 200 officers, helicopters and tracking dogs, the fugitives have not yet been found.
Mr Cuomo said the prison breakout was the first escape from the facility in 150 years.
Power tools used in escape
The New York Post reported that the two men cut through the steel back walls of their cell before clambering along a catwalk to reach a series of pipes and tunnels, which they again cut their way through.
The pair then climbed up through a manhole into a nearby street, "disappearing into the darkness some 20 miles (30 km) south of Canada".
They placed bundles of clothing in their beds to fool guards into believing they were asleep after making their escape on Friday night. Their absence from adjoining cells was not discovered until the following morning.
Mr Cuomo said someone must have heard at least some of the noise. After the prisoners were apprehended, the authorities would conduct a full review of the escape, he added.
"We'll go through the exact details of what they did and how they did it to ensure this never happens again."
Matt was given a jail term of 25 years to life for the kidnapping and beating a man to death in 1997.
Sweat was serving a life sentence without parole for the murder of Broome County Sheriff's Deputy Kevin Tarsia.
Mr Tarsia's brother Steven said finding out that his killer had escaped "turns your world upside-down all over again".
Police are trying to determine how the men acquired the tools needed to carry out the escape.
They may now have crossed the border into Canada or headed to another state, Mr Cuomo said. There was also concern they may have had assistance from someone outside the prison.
Roadblocks have been set up in the area to catch the pair, who both have distinctive tattoos, according to local media.