US Marshal shot and killed in Pennsylvania gunfight ahead of Trump state visit

A United States Marshal has been shot and killed in Pennsylvania, just hours before President Donald Trump is scheduled to visit the state.

The shooting occurred in the state capital Harrisburg, and Mayor Eric Papenfuse said that the shoot out injured three officers, including a local cop.

"Harrisburg mourns the loss this morning of a US Marshal who died protecting our residents. While serving a warrant as part of the US Marshal's task force, three officers were shot, including a Harrisburg police officer, who was wounded," Mayor Eric Papenfuse said in a statement.

Mr Papenfuse continued to say that the officers had returned fire during the gun fight, which occurred at around 6:10 am.

The Harrisburg officer "bravely returned fire and critically injured the gunman," Mr Papenfuse said.

"No words can adequately express the sadness we feel at this moment as we contemplate the loss of yet another law enforcement officer in the line of duty," Mr Papenfuse said. "I extend my sincerest condolences to the family of the slain US Marshal, to his colleagues, and to all law enforcement officers who risk their lives each day to protect and to serve our city and our nation."

Officials provided little other information about the shooting during a morning news conference, but said that one of the other officers had been taken to a nearby hospital and did not have life threatening injuries.

Neighbours told local reporters that they heard dozens of shots Thursday morning.

"Please pray for the police officers injured in Harrisburg this morning. Our police are tough and put their lives on the line everyday to keep communities safe," Congressman Lou Barletta tweeted. "I am praying for a speedy recovery!"

Mr Trump is expected to travel to Pennsylvania Thursday night in an effort to prop up a special election candidate for the House of Representatives in a district that was, until recently, seen as a safe Republican seat. But, with a growing backlash against the President -- laid bare by the Alabama special Senate election last month in which a Democrat won representation for the state for the first time in over 20 years -- the race has become the latest focus as a potential check on Mr Trump.

The President ran on a law and order platform during his election campaign in 2016, and has regularly spoken about the importance of law enforcement safety since becoming President.

The White House did not immediately issue a statement following the shooting in Harrisburg.