Rescue workers were digging through collapsed homes and other buildings in coastal areas of KwaZulu-Natal province on Wednesday, where the death toll stood at 51, officials said.
The region has been hit by heavy rains for days, but authorities did not anticipate the extent of the downpour late on Monday, according to Lennox Mabaso, a spokesman for the provincial cooperative governance and traditional affairs department.
“As a result there was flooding and some structures were undermined and collapsed on people,” said Mr Mabaso, adding that some people were swept away by the water.
KwaZulu-Natal Emergency Medical Services spokesman Robert McKenzie said multiple dwellings and houses collapsed in the mudslides.
Some major roads in and around the port city of Durban were reportedly closed on Wednesday.
Flooding also killed at least three people in the Eastern Cape province, according to state broadcaster SABC.
President Cyril Ramaphosa plans to visit communities in both provinces.
Last week, 13 people were killed during an Easter service in KwaZulu-Natal when a church wall collapsed after days of heavy rains and strong winds.