Two convicted murderers have used power tools to cut through steel pipes at a maximum-security prison near the US-Canada border - and escape through a manhole.
Police say the elaborate plan also involved a hole being cut out of the back of a cell, and a route through tunnels.
Major Charles Guess - from New York State Police - says more than 200 officers are involved in the search:
The two men - Richard Matt, 48, and David Sweat, 34 - were not present for a Saturday morning bed check at the Clinton Correctional Facility in Dannemora, about 20 miles (32km) from the Canadian border.
Authorities stressed that no one should approach the men, who are considered a danger to the public.
New York Governor Andrew Cuomo cancelled plans to attend Saturday's Belmont Stakes horse race to attend a briefing about the manhunt, his office said.
Police have set up roadblocks around the Dannemora area and were asking people to be on the lookout.
Matt - who has a tattoo reading Mexico Forever - was serving 25 years to life for three counts of murder, kidnapping and robbery.
Sweat was serving a life sentence without the possibility of parole for the murder of a sheriff's deputy.
