Two people have died and 16 others are injured after a balcony at a South Korean nightclub attended by World Championship swimming athletes collapsed.

Hundreds were at the event in the southern city of Gwangju when the collapse occurred next to the athletes' village for the ongoing FINA World Swimming Championships.

Police confirmed the two people killed were South Korean men aged 38 and 27. They were not athletes involved in the competition.

Among the 16 injured, 10 are foreign, while eight are athletes who were competing in Gwangju.

Police stand at the door to a nightclub in Gwangju, South Korea Credit: Lee Jin-man/AP

Among the athletes include three Americans, two New Zealanders, one Dutch, one Italian and one Brazilian, a police officer said.

He added most had minor injuries but an American female water polo player had to undergo surgery.

The two other Americans - a man and a woman - are also water polo players.

The nightclub's co-owners have been detained and three other club officials have been summoned as police investigate with the collapsed balcony was an unauthorised structure.

Christopher Ramsey, chief executive officer of USA Water Polo, said: "This is an awful tragedy.

The World Swimming Championships are currently ongoing in the city of Gwanju, South Korea. Credit: AP

“Players from our men’s and women’s teams were celebrating the women’s world championship victory when the collapse occurred at a public club. Our hearts go out to the victims of the crash and their families.”

US water polo player Kaleigh Gilchrist suffered a deep left leg cut and underwent surgery at a hospital in Gwangju, said Greg Mescall, director of communications for USA Water Polo.

He said that Paige Hauschild suffered cuts on the right arm and Johnny Hooper on the left hand that required stitches.

Ben Hallock suffered minor scrapes on the legs, he said.

Rescue workers inspect the collapsed balcony Credit: Shin Dae-hee/Newsis via AP/PA

The anti-disaster agency said the injured also included two Uzbekistan exchange students. None of the injured is in life-threatening condition.

Members of the New Zealand men’s and women’s water polo teams were also at the nightclub. The men’s captain, Matt Small, described a chaotic scene and said that his team tried to help the injured.

“(It was) business as usual and then it literally collapsed beneath our feet,” Mr Small said, speaking to New Zealand Radio Sport by phone.

“None of the boys are hurt or injured though — so that’s good. But everyone’s a bit shaken up at the moment.

“We did what we could but we couldn’t really do too much. Some of them were pretty dire cases.

“We were more so just concerned about everyone else, we were trying to do a number count and make sure all the boys were there.”

Of the eight athletes injury, a committee statement said seven of them had already returned to the athletes’ village after minor treatments at hospitals.