The death toll from a gas tanker blast in Johannesburg on Christmas Eve has climbed to 34, the provincial health department said on Friday.

"The Department of Health can confirm that the death toll from Boksburg Explosion incident has risen to 34 as of Friday," 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.

South African President Cyril Ramaphosa has promised relief to the victims and said authorities were investigating the incident.

(With input from Reuters)