Investigators evaluate the scene of a shooting at an Airbnb rental property in Pittsburgh on Sunday. AP

Authorities in South Carolina are investigating a shooting at a nightclub early on Sunday that wounded at least nine people. It was the second mass shooting in the state and the third in the nation during the Easter holiday weekend.

The shootings in South Carolina and one in Pittsburgh, in which two minors were killed early Sunday, also left at least 31 people wounded.

No one was reported killed in the violence at Cara’s Lounge in Hampton County, roughly 80 miles (130 kilometres) west of Charleston, according to an email from South Carolina's State Law Enforcement Division, which is investigating the shooting. A phone call to the nightclub was not answered.

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Shots fired at a house party in Pittsburgh early Sunday killed two 17-year-olds and wounded at least eight other people, police said.

According to the report two male gunshot victims died at the hospital. The Allegheny County Medical Examiner’s Office identified them as Jaiden Brown and Mathew Steffy-Ross, both 17.

Authorities in South Carolina say they are investigating shooting at a club in Hampton County on Sunday. AP

Eight people were also being treated for gunshot wounds, and others were injured trying to escape, Schubert said, including two who broke bones after jumping from windows. One victim was injured after a car was "shot up,” Schubert said.

George Stevens said he was outside a bar next door to the rental property smoking a cigarette when he heard what he thought were fireworks, then saw kids fleeing.

Hundreds of people — the "vast majority” of them minors — had gathered at a short-term rental property when some kind of altercation occurred and shots were fired at around 12:30am, Pittsburgh Police Chief Scott Schubert said at a midday news conference.

Schubert said there was gunfire both inside and outside the rental home, "and potentially back and forth." Bullet casings found at the scene indicating handguns and one rifle were used, he said, and police believe there were multiple shooters.

Police tape, broken glass, and bloodstains outside an Airbnb apartment rental in Pittsburgh, Pennsylvania. AFP

Investigators believe there were multiple shooters, and Schubert said police were processing evidence at as many as eight separate crime scenes spanning a few blocks around the rental home.

The two shootings come just a day after gunfire erupted at a busy mall in the South Carolina state capital of Columbia, about 90 miles (145 kilometres) north of Sunday's nightclub shooting. Nine people were shot, and five people sustained other kinds of injuries while trying to flee the scene at the Columbiana Centre, Columbia Police Chief W.H. "Skip” Holbrook said Saturday. The victims ranged in age from 15 to 73. None faced life-threatening injuries.

"We don’t believe this was random,” Holbrook said. "We believe they knew each other and something led to the gunfire.”