A manhunt was launched after a gunman shot two police officers in an ambush in Pennsylvania.
One officer was killed and another injured in the shooting which happened early on Thursday local time in south-west Pennsylvania, about 25 miles from Pittsburgh.
Police and the town’s mayor told residents to stay indoors as they launched a search for the shooter, local media reported.
One witness said on Twitter they saw an officer lying shot on the ground.
The mayor of Canonsburg, Dave Rhome, confirmed on an American radio station that two officers had been shot.
Local media reported Special Weapons and Tactics police arrived on the scene to hunt for the gunman.
One of the officers was flown to hospital in Pittsburgh while the other was taken to a hospital in the town of Canonsburg. Details of their injuries are not known.
Authorities in the US have not yet said what led to the shooting.
State police spokeswoman Melinda Bondarenka told reporters the incident began at 3.14am when the Canonsburg officers responded to a report of a domestic dispute.
The officers were "ambushed upon their arrival" and immediately shot, Ms Bondarenka said.
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