At least a dozen people were killed in Johannesburg on Tuesday night after more than 10 gunmen stormed an informal settlement and opened fire, the South African police said.

Investigators started a manhunt and on Wednesday were still trying to determine a motive for the shooting, according to a statement from Col. Dimakatso Nevhuhulwi. At least nine people had gunshot wounds and were seeking treatment at area hospitals, Colonel Nevhuhulwi said.

The police received a call about a shooting in progress shortly after 11 p.m. on Tuesday, they said, and officers arrived to find numerous victims with gunshot wounds. The gunmen had been dropped off in a minibus taxi, Colonel Nevhuhulwi said, “and moved through the area opening fire on residents and community members at multiple locations before fleeing the scene in the same vehicle.”

Nine of the people killed were men, and three were women, the police said.

Speaking to a local television news station with his face covered, a man who said he was a resident of the settlement said he believed the attack was linked to a dispute between illegal miners. After a disagreement, some miners left the community, he told the station, Newzroom Afrika. Those disgruntled miners had previously returned several times to cause harm but were unsuccessful, he said.

The man said he believed he knew who the shooters were but was anxious about sharing information with the authorities out of fear of getting in trouble with the police. Many illegal miners in South Africa, known as zama zamas, are undocumented immigrants often targeted by law enforcement.

“If there is honesty within our police and they can be trusted, we can explain even where to find the shooters because we know them,” the man said.

The settlement, Jumpers, in the east of Johannesburg, is a collection of small shacks made of tin and wood, tightly packed to form narrow alleys that create something of a maze. The police said that there were two entrances to the settlement.

South Africa long has struggled with mass shootings and has one of the highest murder rates in the world. The shooting happened hours after the police commissioner for Gauteng, the province that includes Johannesburg, announced that murders in the province had decreased by 15 percent in the first quarter of this year.

Zimasa Matiwane contributed reporting from Johannesburg.