Gunmen stormed an informal settlement in Johannesburg and shot 12 people dead overnight, South African police said on Wednesday, in the latest mass shooting in the country.

The shootings happened before midnight on Tuesday in an impoverished shantytown of metal and wooden shacks near where illegal miners were living and working, police said.

Around 10 attackers were driven to the Jumpers settlement and dropped off before storming the area, a police spokesperson said.

"The suspects allegedly entered the informal settlement through both entrances and moved through the area, opening fire on residents and community members at multiple locations before fleeing the scene in the same vehicle," the spokesperson said.

"Preliminary investigations reveal that 12 people died as a result of the attack," Colonel Dimakatso Nevhuhulwi said.

"Eight adult males and three adult females were declared dead at the scene," she said. One person died in hospital.

Illegal mining

South Africa is awash with legal and illegal firearms and shootings are common, often fuelled by gang rivalry and competition between informal businesses.

The attack was in an area about six kilometres east of Johannesburg’s city centre and near abandoned gold mines.

Police said the motive was not yet known and no arrests had been made, but there were suspicions it was related to competition over illegal mining in the area.

"As you know, this area is adjacent to the illegal mining area. We are having those suspicions," provincial commissioner Lieutenant General Tommy Mthombeni told reporters at the scene.

"One can term this incident to be insane, to be heartless and to an extent, it is barbaric," he said.

Mthombeni said police had swept the area three weeks ago and confiscated guns and ammunition for AK-47 rifles, arresting three people.

Police did not give details about who was killed but a resident told the eNCA broadcaster that people from the neighbouring country, Lesotho, lived in the settlement.

A local ward councillor who visited the scene said the attackers first opened fire on a shack built over an informal mine shaft before moving on to nearby taverns, the Sunday World media site reported.

"It looked like a well-planned ambush that was very targeted," Neuren Pietersen was quoted as saying.

After the attack, authorities were seen hauling away equipment believed to be linked to illegal mining activities.

Illegal mining in South Africa draws people from across southern Africa and has been linked to organised crime, assassinations, extortion and other illegal activities.

Clandestine artisanal miners have become an entrenched presence around Johannesburg and its satellite settlements along the gold reef.

Driven by poverty and unemployment, the zama zamas - which means "those who try" in the Zulu language - descend deep into still gold-bearing shafts abandoned by mining companies.

In a mass shooting linked to rivalry between illegal mining gangs, nine people were killed in December when gunmen opened fire at a bar in the Bekkersdal township southwest of Johannesburg.

In March, soldiers moved into violence hotspots in Johannesburg to support police efforts to tackle rampant crime, described by President Cyril Ramaphosa as one of the biggest threats facing the country.