Five people have been killed in a shooting at a garden party in Pennsylvania and at least two gunmen are at large, police have said.

Four women and a man were gunned down late on Wednesday during the party in Wilkinsburg, a Pittsburgh suburb. At least three others were in a stable or critical condition in hospital.

A motive was not immediately known.

Lieutenant Andrew Schurman of Allegheny County homicide unit said the gunmen barged into the party and opened fire in an ambush-style attack.

Resident Kayla Alexander told WPXI-TV she heard a more than 20 gunshots in the usually-quiet neighbourhood.

People gathered on the street, some of them sobbing and saying they lost family members.