Manhunt underway after ambush leaves US state trooper dead and second injured in Pennsylvania

State police Commissioner Frank Noonan, addresses the media after two troopers were ambushed outside a state police barracks in northeastern Pennsylvania. (AP Photo/Scranton Times & Tribune, Butch Comegys)

A manhunt is underway after a state trooper was shot dead at a US police barracks in Pennsylvania.

The gunman – or possibly a team of shooters – opened fire at about 11pm on Friday, killing one trooper and injuring another, at Blooming Grove Barracks in Pike County.

Police were still on the hunt for the unknown assailant on Saturday morning. They have since questioned a man, said to be a person of interest, about the shooting but have made no arrests.

Pennsylvania State Police Commissioner Frank Noonan said during a morning news conference: “I know a lot of people are wondering if the threat is resolved. It is not.

“The individual who perpetrated this heinous crime is still at large.” He added: "It's been an emotional night for all of us."

Noonan said the troopers were ambushed during a late-night shift change, but did not go into further detail.

The injured trooper has undergone surgery to treat his wounds and is said to be in a stable condition, though he did not disclose the names of either victims.

According to some media reports, local roads around the area have been sealed off while more than 100 police vehicles, including helicopters and a SWAT team searched for those responsible.