The blast tore the roof off the emergency department at the Tambo Memorial hospital in the city's Boksburg suburb on Saturday, while also injuring scored of bystanders, destroying houses and several cars.
"The Department of Health can confirm that the death toll from Boksburg Explosion incident has risen to 34 as of Friday, 30 Dec. 2022," a spokesperson for the Gauteng Department of Health said in a statement.
The victims include 11 health workers and 23 members of the public, the spokesperson said, adding that the numbers were constantly being updated.
The severe nature of the burns inflicted by the blast was expected to result in an increase in the number of deaths, authorities had earlier said.
Victims included children as young as nine, according to a message shared by the health department on social media commemorating a memorial for the victims.
Families and friends of the victims, along with health minister Joe Phaahla gathered in the Boksburg Civic Centre on Friday morning for a memorial service and paid their respects by lighting candles.
President Cyril Ramaphosa has promised relief to the victims and said authorities were investigating the incident.