Shots fired at a house party early Sunday left two under-age people dead and at least nine more injured, police in the US said.

The shooting happened at about midnight during a party at a property in Pittsburgh, Pennsylvania, where there were more than 200 people inside, many of them underage, police said.

At least 11 people were being treated for gunshot wounds and two male victims died at hospital, police said.

Others were injured attempting to flee, with at least two people suffering broken bones by jumping out of the building’s windows, authorities said.

Officers reported hearing shots in the area and seeing several young people fleeing the area on foot and in vehicles, police said.

Police said as many as 50 rounds were fired inside and several more were fired outside.

Shell casings from rifles and pistols were found at the scene, Pittsburgh police commander John Fisher said.

Police are processing evidence at as many as eight separate crime scenes around the shooting scene, police said.

“You have alcohol, you have underage people here and you have guns – that’s a deadly combination at any type of an event, and the end result is it’s a tragedy,” Mr Fisher said.