At least 16 people, including children, have died after a gas leak at a South African slum near Johannesburg, emergency services said Thursday, revising the death toll after some people were resuscitated.

The Wednesday night disaster, thought to be linked to illegal mining activities, occurred at the Angelo informal settlement east of Johannesburg.

"We have got 16 on scene now that are confirmed dead, and the intervention of paramedics managed to revive some others and they were taken to hospital," emergency services spokesman William Ntladi told AFP from the scene.

Of those in hospital, four are in "critical" condition while 11 are in "serious but stable" condition, he said. One, who he described as a minor, was fully conscious, he added.

Five women and three children were among the dead.

Fire and emergency services received a call around 8 pm (1800 GMT) about a gas explosion, but on arrival they discovered it was "a gas leakage from a cylinder" containing a "poisonous gas", Ntladi said.

In a statement he said the cause of the incident "is alleged to be a nitrate oxide gas leakage from the cylinder used in an illegal mining activity in and around the settlement."

"Apparently, the illegal miners used the gas to extrapolate gold out of the soil," he said.

Upon arriving at the scene near the middle-class suburb of Boksburg, first responders found scores of people "lying all over the area due to inhalation of this toxic gas," Ntladi said in the statement.

Abandoned mine 

Rescue workers and forensic police combed through the affected area -- a cluster of squalid shacks built out of bricks and corrugated iron sheets -- late into the night, AFP journalists saw.

The area sits at the foot of an old and abandoned mine.

Neighbours gathered around a fire during the cold southern hemisphere winter, watching the stream of uniformed police officers and forensic investigators at work.

With a dizzying unemployment rate of more than 32 percent, South Africa is home to thousands of illegal miners nicknamed "zama zamas" which means "those who try their luck" in Zulu.

Thousands of unregistered miners scavenge obsolete mines for gold under arduous and often perilous conditions.

South Africa's commercial hub Johannesburg and its surrounding areas are built around mountainous dumps of soil and cavernous pits left behind by generations of mining companies that started extracting during a gold rush in the 1880s.

Boksburg was last month struck by a 5.0 magnitude earthquake, suspected to have been linked to the maze of underground tunnels and shafts associated with illegal mining in the area.

The same suburb was also the scene of a massive gas tanker explosion that killed 41 people on Christmas Eve last year when a truck carrying liquefied petroleum gas (LPG) got stuck under a bridge, triggering a leak and blast.

Among the victims were people and medics who had approached the scene either to help or see the trapped truck.

Dozens at a nearby hospital, including patients and staff members, sustained serious burns after the explosion, which smashed windows and caused the roof to collapse.