(CNN) The manhunt for two escaped murderers took authorities to southwestern New York on Saturday.

State Police said they were following leads in Allegany County in the search for Richard Matt, 48, and David Sweat, 35

A law enforcement source briefed on the prisoner investigation told CNN there was a credible sighting of the escapees near the town of Friendship, just north of the Pennsylvania border.

State police, however, called it an " unconfirmed sighting ."

The sheriff's office said someone called in a tip that led authorities to tracks that police were following to see whether they led to the two convicted killers.

Heavily armed police and law enforcement agents were walking along a railroad near Friendship, another source told CNN. State police said two men were spotted near the rail line earlier.

CNN affiliate WIVB in Buffalo sent one of its reporters to Friendship, where she was asked to leave the search area because state police said it was a "hot spot."

State trooper just instructed us to leave East Maple Grove area, called it "hot spot." Chopper circling over bridge. — Jenn Schanz (@JennSchanz4) June 20, 2015

Emergency services radio traffic monitored by CNN indicated police were moving large numbers of officers into the area. Responding officers were asked at one point to maintain radio silence.

Photos: Manhunt for escaped New York prisoners Photos: Manhunt for escaped New York prisoners Richard Matt, left, and David Sweat were on the run after they escaped from the Clinton Correctional Facility in Dannemora, New York, on Saturday, June 6. Matt was killed by police on Friday, June 26. Sweat was captured two days later and is now in police custody. Hide Caption 1 of 34 Photos: Manhunt for escaped New York prisoners Hide Caption 2 of 34 Photos: Manhunt for escaped New York prisoners Matt's body lies on the ground after he was killed by police on June 26. Hide Caption 3 of 34 Photos: Manhunt for escaped New York prisoners Sweat was captured on June 28, multiple law enforcement sources briefed on the investigation told CNN. He was shot twice in a field by a New York state trooper and taken into custody in upstate New York, close to the Canadian border. Hide Caption 4 of 34 Photos: Manhunt for escaped New York prisoners Sweat is bloodied, shirtless and cuffed at the ankles, and he appears to be breathing into an oxygen mask after his capture on June 28. Hide Caption 5 of 34 Photos: Manhunt for escaped New York prisoners Police escort ambulances from an area where law enforcement officers were searching for Sweat on June 28. Hide Caption 6 of 34 Photos: Manhunt for escaped New York prisoners Law enforcement officials are seen in the side-view mirror of a car as they stand guard June 28 in Duane, New York. Hide Caption 7 of 34 Photos: Manhunt for escaped New York prisoners FBI agents conduct a search for Sweat near Duane on June 28. Hide Caption 8 of 34 Photos: Manhunt for escaped New York prisoners An FBI agent searches for Sweat on June 28. Hide Caption 9 of 34 Photos: Manhunt for escaped New York prisoners Department of Corrections officers man a roadblock in Malone, New York, on Saturday, June 27. Hide Caption 10 of 34 Photos: Manhunt for escaped New York prisoners New York State Police officers talk to motorists at a roadblock near Malone on June 27. Hide Caption 11 of 34 Photos: Manhunt for escaped New York prisoners New York State Police officers stand guard near the site where Matt was shot and killed in Malone on June 26. Hide Caption 12 of 34 Photos: Manhunt for escaped New York prisoners A New York State Police officer stands guard near the shooting scene in Malone on June 26. Hide Caption 13 of 34 Photos: Manhunt for escaped New York prisoners Department of Corrections officers and a forest ranger, back, search a barn in Owls Head, New York, on June 26. Hide Caption 14 of 34 Photos: Manhunt for escaped New York prisoners Corrections officers stop a vehicle Monday, June 22, in Owls Head, about 20 to 25 miles west of the prison where Matt and Sweat escaped. The discovery of the escapees' DNA in a cabin re-energized the search for the fugitives. Hide Caption 15 of 34 Photos: Manhunt for escaped New York prisoners A bus transports corrections officers to a search area in Mountain View, New York, on June 22. Hide Caption 16 of 34 Photos: Manhunt for escaped New York prisoners Law enforcement officers use all-terrain vehicles in Mountain View on June 22. Hide Caption 17 of 34 Photos: Manhunt for escaped New York prisoners Corrections officers search railroad tracks near Friendship, New York, on Sunday, June 21, after a possible sighting of the fugitives. Hide Caption 18 of 34 Photos: Manhunt for escaped New York prisoners New York State Police officers gather along Route 20 near Friendship on June 21. Hide Caption 19 of 34 Photos: Manhunt for escaped New York prisoners A task force of U.S. Marshals and police officers go door to door near Dannemora, New York, searching for the two escaped murderers on Tuesday, June 16. Hide Caption 20 of 34 Photos: Manhunt for escaped New York prisoners New York State Troopers stop civilian cars at a checkpoint outside Dannemora on Monday, June 15. Hide Caption 21 of 34 Photos: Manhunt for escaped New York prisoners Prison tailor Joyce Mitchell, charged with aiding the escape, appeared in court on Monday, June 15. Hide Caption 22 of 34 Photos: Manhunt for escaped New York prisoners Department of Corrections officers work a roadblock in Saranac, New York, on Saturday, June 13. Hide Caption 23 of 34 Photos: Manhunt for escaped New York prisoners Law enforcement personnel line the roadside on June 13 as they search an area in Cadyville, New York. Hide Caption 24 of 34 Photos: Manhunt for escaped New York prisoners New York State Police prepare equipment during the search on Thursday, June 11. Hide Caption 25 of 34 Photos: Manhunt for escaped New York prisoners Authorities block a road in Cadyville during the manhunt on June 11. Hide Caption 26 of 34 Photos: Manhunt for escaped New York prisoners A Vermont state trooper heads out on Lake Champlain in Burlington, Vermont, on June 11. Hide Caption 27 of 34 Photos: Manhunt for escaped New York prisoners Law enforcement officers question a woman who lives near the Dannemora prison on Wednesday, June 10. Hide Caption 28 of 34 Photos: Manhunt for escaped New York prisoners An employee stands guard at the Clinton Correctional Facility on June 10. Hide Caption 29 of 34 Photos: Manhunt for escaped New York prisoners An officer checks the trunk of a car at a checkpoint near the Dannemora border on June 10. Hide Caption 30 of 34 Photos: Manhunt for escaped New York prisoners Officers continue their search in Essex, New York, on Tuesday, June 9. Hide Caption 31 of 34 Photos: Manhunt for escaped New York prisoners An officer walks through a swampy area near Essex on June 9. Hide Caption 32 of 34 Photos: Manhunt for escaped New York prisoners Law enforcement officers search a wooded area in Dannemora on Monday, June 8. Hide Caption 33 of 34 Photos: Manhunt for escaped New York prisoners State corrections officers monitor traffic June 8 at the Clinton Correctional Facility. See photos of the route the escaped prisoners took Hide Caption 34 of 34

Police were pursuing other possible sightings of the two men, who broke out from Clinton Correctional Facility in upstate New York.

Possible sightings happened last weekend in Steuben County, about 45 miles east of Friendship, state police said in a news release Friday evening.

"Witnesses spotted two men on June 13 walking near the Gang Mills railyard on Rita's Way in the town of Erwin," police said. "The next day, two men with the same description were spotted walking along County Route 115 in the town of Lindley, heading toward the Pennsylvania border."

JUST WATCHED Could tracks belong to the escaped killers? Replay More Videos ... MUST WATCH Could tracks belong to the escaped killers? 01:11

The unconfirmed sightings came from two separate individuals, police spokesman Beau Duffy told CNN on Saturday.

The sightings were not reported to New York State Police until Tuesday. State police sent investigators at that time to the areas to conduct interviews, according to Duffy.

Investigators have collected "inconclusive" surveillance camera video that is being sent for further analysis.

On Saturday, police urged people living in the Allegany County area along the New York-Pennsylvania border to be on alert for Matt and Sweat, both of whom have killed in the past.

"Do not approach, as both are considered to be very dangerous," officials warned.

In another development, the state corrections department said a corrections officer was placed on administrative leave as part of the investigation into the escape. The officer's name was not released.

The district attorney declined to comment but said the corrections officer was male.

Most wanted list

The U.S. Marshals Service has added Matt and Sweat to its list of the 15 most wanted fugitives and offered a $50,000 reward for information leading to their capture.

The list "is reserved for the worst of the worst," said U.S. Marshals Service Director Stacia Hylton. "There is no question David Sweat and Richard Matt fall into this category."

Authorities warned Friday that the search could take some time as the massive manhunt enters another week.

"We're configured now for a rapid response," New York State Police Maj. Charles Guess said at a news conference.

"We'd like nothing more than to place them into custody today. ... However, we're also geared for the long haul, the state police and our partners. ... We're no strangers to lengthy months and yearlong investigation."

The U.S. Marshals Service has added Richard Matt, left, and David Sweat to its list of the 15 most wanted criminals.

As many as 800 law enforcement officers have participated in the manhunt, which has cleared nearly 200 abandoned buildings, hundreds of occupied homes and more than 600 miles of rural trails, officials said.

"We're not going anywhere," Guess said. "Our plan is to pursue these men relentlessly until they are in custody."

Back at the prison, the breached prison cell walls, steam tunnels and pipes and other areas involved in the escape have been repaired, and a lockdown has been lifted, according to Daniel Martuscello, a deputy commissioner of the state corrections department.

State police have asked hunters and homeowners with surveillance cameras to check their footage all the way back to June 6, the day of the prison break, for any unusual activity.

The search has reached all the way to the borders Canada and Mexico, where wanted posters of the escaped killers are being handed out.

Questions over Joyce Mitchell

New details are emerging about the relationships between the convicts and prison tailor shop instructor Joyce Mitchell, who has been charged for aiding in escape.

Her husband, also a prison employee, feels betrayed by what happened, his attorney says.

Joyce Mitchell, 51, is behind bars, accused of helping the inmates break free and sneaking hacksaw blades, chisels, drill bits, a punch and other contraband into the convicts' hands before they broke out.

Authorities have said Matt had a sexual relationship with Mitchell.

No court date has been set for Mitchell, who has pleaded not guilty to the two charges brought against her and has been talking to authorities. If convicted, Mitchell could face up to eight years behind bars.

Mitchell's husband, Lyle, also worked in the prison's tailoring block.

But the prosecutor said Wednesday that Lyle Mitchell didn't know about the prisoners' escape plan before it happened and wasn't aware of his wife's relationships with the inmates.