Most of the deaths were in KwaZulu-Natal province. Flooding also killed at least three people in neighbouring Eastern Cape province, state broadcaster SABC said on Wednesday.

KwaZulu-Natal Emergency Medical Services spokesman Robert McKenzie said the rains mainly hit areas around the port city of Durban, and multiple dwellings collapsed in mudslides.

Rescue workers were digging through collapsed buildings on Wednesday.

Victor da Silva, a resident of the coastal town of Amanzimtoti, said his family managed to evacuate before the floods destroyed their home and cars.

"On Monday, the water was just crazy. And yesterday morning I got here, everything was fine, my garage was still here, the other part of the house was still here, and it just couldn't stop raining," Da Silva said.

"And then an hour and a half later, everything poof (vanished) because the rain just hasn't stopped."

Authorities in southern Tanzania ordered evacuations of residents from low-lying areas and the closure of schools and offices ahead of landfall of Tropical Cyclone Kenneth on neighbouring Mozambique's coast on Thursday.

The region had been hit by heavy rains for days, but authorities did not foresee the extent of the downpour late on Monday, spokesman for the provincial Cooperative Governance and Traditional Affairs department Lennox Mabaso said.

President Cyril Ramaphosa visited affected communities in KwaZulu-Natal on Wednesday and was expected in the Eastern Cape in the next few days.

"This is partly what climate change is about, that it just hits when we least expect it," he said.

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.

Australian Associated Press