Police in three states were searching on Saturday for a gunman or gunmen who shot and killed a state trooper in an ambush at a police barracks in Pennsylvania, police said.

The shooting, in which a second trooper was wounded, occurred at the Blooming Grove barracks around 11 p.m. EDT on Friday, said Pennsylvania State Police Commissioner Frank Noonan during a morning news conference.

The shooter or shooters were still on the loose on Saturday morning, Noonan said, prompting a manhunt by police from Pennsylvania, New York and New Jersey.

"I know a lot of people are wondering if the threat is resolved. It is not," he said. "The individual who perpetrated this heinous crime is still at large."

Noonan said police do not have a description or any information on the identity of the shooter or shooters.

Noonan said the troopers were ambushed, but would not share details of the incident given that it is an ongoing investigation.

The wounded trooper had undergone surgery and was in a stable condition, according to Noonan, who did not disclose the names of the victims.

Footage on local television station WNEP showed police cruisers and SWAT vehicles rushing to the scene while a helicopter hovered overhead.

Blooming Grove is a township of roughly 5,000 people near the New York state border.