The Wednesday night disaster, thought to be linked to illegal mining activities, occurred at the Angelo informal settlement near the district of Boksburg, 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, France 24 reported.
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.
"Due to the scene still unfolding we are busy checking the entire area affected to ascertain numbers of hospitalized casualties," he said earlier.
Preliminary information suggests the gas was being used "as part of illegal mining activities," he added.
With a dizzying unemployment rate of more than 32 percent, South Africa is home to thousands of illegal miners. Thousands of the unregistered miners scavenge obsolete mines for gold under arduous and often perilous conditions.
MP/PR
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