Authorities in the US state of South Carolina are investigating a shooting at a nightclub that wounded at least nine people.

The mass shooting early on Sunday was the second in the state and the third in the United States during the Easter holiday weekend.

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

No one was reported killed in the violence at Cara’s Lounge in Hampton County, about 130 kilometres west of Charleston, according to an email from South Carolina’s State Law Enforcement Division, which is investigating the shooting.

In Pittsburgh, two male youths were killed and at least eight people wounded when shots were fired during a party at a short-term rental property.

The “vast majority” of the hundreds of people at the party were underage, the city’s Police Chief Scott Schubert told reporters.

Investigators believe there were multiple shooters, and Mr 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 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 on Saturday.

The victims ranged in age from 15 to 73. None faced life-threatening injuries.

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

The only person arrested in the mall shooting so far is Jewayne Price, 22, one of three people initially detained by law enforcement as a person of interest.

Price’s attorney, Todd Rutherford, told news outlets on Sunday that his client fired a gun at the mall, but in self-defence.

Mr Rutherford said Price faces a charge of unlawfully carrying a pistol because he legally owned his gun but did not have a permit to carry a weapon.

The three Easter weekend mass shootings are in addition to other gun violence in recent days.

Last week, a gunman opened fire in a New York subway car, wounding 10 people. A suspect was arrested the next day.

Earlier this month, six people were killed and 12 others wounded in Sacramento, California, during a gunfight between rival gangs as bars closed in a busy downtown area just blocks from the state Capitol.

One week ago, a shooting inside a crowded nightclub in Cedar Rapids, Iowa, left a man and a woman dead and 10 people wounded.

And last month, 10 people were shot at a spring break party in Dallas and several others were injured as they tried to escape the gunfire.