Ten gunmen stormed an informal settlement on the outskirts of Johannesburg late Tuesday and shot dead 12 people, police said Wednesday. The attackers arrived in a vehicle, entered the Jumpers settlement from both sides, and opened fire at multiple locations before fleeing.

Eight men and three women were killed at the scene. One more person died in hospital. Police haven't made any arrests and say the motive is still unclear, but they suspect it's connected to illegal mining in the area.

The settlement sits about six kilometres east of central Johannesburg, near an abandoned gold mine. It's home to many people from neighbouring countries, including Lesotho. Police say illegal miners — known locally as zama zamas, meaning 'those who try' in Zulu — operate in the area, descending into old mine shafts left by companies.

“At this stage, we couldn't determine what is the motive,” said Lieutenant General Tommy Mthombeni, the provincial police commissioner. “As you know, this area is adjacent to the illegal mining area. We're having those suspicions.” He called the attack “insane, heartless and barbaric.”

South Africa has a serious problem with illegal firearms, and shootings are common. Gang rivalry and competition over informal businesses often fuel the violence. Three weeks ago, police swept the same area and seized guns and ammunition for AK-47 rifles. They also arrested three people.

This isn't the first mass shooting linked to illegal mining gangs. In December, nine people were killed when gunmen opened fire at a bar in Bekkersdal township, southwest of Johannesburg, another gold-mining area.

In March, President Cyril Ramaphosa deployed soldiers to violence hotspots in Johannesburg to support police efforts against rampant crime, which he's described as one of the biggest threats facing the country.

Police at the scene on Wednesday were seen hauling away equipment believed to be linked to illegal mining. Illegal mining in South Africa draws people from across southern Africa and has been linked to organised crime, assassinations, and extortion. Driven by poverty and unemployment, the zama zamas risk their lives in dangerous, abandoned shafts to extract gold.

Colonel Dimakatso Nevhuhulwi confirmed the death toll: “Eight adult males and three adult females were declared dead at the scene.” One victim died later in hospital. The attack happened just before midnight on Tuesday.

Residents told local broadcaster eNCA that many of the victims were from Lesotho. The settlement is made up of metal shacks, and living conditions are poor.

Police are appealing for anyone with information to come forward. The investigation continues.