At least 17 people, including three children, were killed after toxic nitrate gas leaked from a cylinder in an informal settlement near Boksburg east of Johannesburg, South Africa.
Gauteng Province Premier Panyaza Lesufi said investigations were under way to determine how the leak happened and what type of gas was involved. Bodies of the victims of the leak were scattered over the area, Mr Lesufi said.
"The scene was heartbreaking," he said, adding that one person had died in a hospital overnight.
The three children killed in the gas leak were aged one, six, and 15, the police said.
Four people were rushed to the hospital in a "critical" condition while 11 were in a "serious but stable" state, emergency services spokesman William Ntladi told AFP. One of the injured, who he described as a minor, was fully conscious, he added.
Search teams were still looking for other casualties with the bodies of the victims lying on the ground hours after the leak as emergency services awaited forensic investigators.
The emergency services spokesperson: "We can't move anybody. The bodies are still where they are on the ground."
He said the gas leaked from a nitrate gas cylinder that was kept in a shack and authorities believed it was being used by illegal miners to separate gold from dirt and rock.
Mr Lesufi tweeted videos of the dusty inside of a shack where at least four gas cylinders can be seen on metal stands.
Forensic workers in hazmat suits combed the area on Wednesday night and will continue their investigations on Thursday and try to secure the area, the premier said.
“They’ve tried to ensure that those cylinders that are still there cannot either explode or they cannot harm people further,” he said. “When I came here last night the smell was still up in the sky.”
A spokesperson for the Disaster and Emergency Management Services in Ekurhuleni municipality, where the disaster occurred, linked the tragedy to illegal mining.
"Whether the illegal miners are among the deceased, that is not yet known," William Ntladi told broadcaster SABC, which gave no further details.
Gold-rich areas around Johannesburg are home to thousands of illegal miners nicknamed "zama zamas", who go into closed-off and disused mines to search for any deposits left over.
The middle-class suburb of 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.
On Christmas Eve, 41 people died in Boksburg after a truck carrying liquefied petroleum gas got stuck under a bridge and exploded.
A methane gas explosion in a disused South African mine killed at least 31 people believed to be from neighbouring Lesotho in May.
