Washington: A gunman who opened fire in a courthouse building in the US state of Pennsylvania and injured four people, has been shot dead by the police, authorities said.

The gunman entered the Masontown Borough Municipal Centre at around 2 pm on Wednesday and began firing, CNN quoted Lt. Steve Dowlin of the Pennsylvania State Police.

The four victims included a sergeant from the Masontown police department. Their injuries are not life-threatening, Dowlin said.

The suspect had a restraining order against him related to a choking case that was to be heard on Wednesday afternoon, Fayette County District Attorney Richard Bower said.

The suspect had been charged with strangulation, aggravated assault, extremist threats and simple assault as a result of a domestic matter several weeks ago, Bower added.

The motive behind the attack and the gunman's identity remains unknown.

Masontown is in southern Pennsylvania, about 55 miles from Pittsburgh and 20 miles north of Morgantown, West Virginia. The town has about 3,300 residents.