New York state officials are investigating whether a civilian staff member or contractor helped a pair of convicted murders to escape from a maximum-security prison near the Canadian border, Governor Andrew Cuomo said on Monday.

Several hundred law enforcement officials were in their third day of searching for Richard Matt, 48, and David Sweat, 34, who went missing from the Clinton Correctional Facility in Dannemora, about 20 miles (30 km) south of the Canadian border.

"I would be shocked if a guard was involved, and that's putting it mildly," Cuomo told CNN. "But we're looking at the civilian employees now and the private contractors to see if possibly if a civil employee or contractor was assisting the escape because they wouldn't have equipment on their own, that's for sure."

A female employee of facility was interrogated by investigators who viewed her as a possible accomplice, the New York Post reported on Monday, citing unidentified sources.

New York is offering a $100,000 reward for information leading to the apprehension of the men it describes as dangerous and have notified law enforcement in Canada and Mexico about the fugitives, the first to escape in the prison's 150-year history.

The pair are believed to have cut through the steel walls at the back of their adjoining cells and escaped through a steam pipe. They left behind a note reading "have a nice day."

Cuomo warned that the pair could have traveled a great distance since escaping: "They could be literally anywhere in the country now, these are really dangerous individuals."