Up to 10,000 people in the South African coastal resort of Knysna have been evacuated as wildfires fanned by strong winds ripped through the town, destroying homes and other properties, officials said.

Eight people have been killed, three of them in the Knysna area, as the worst storm to hit Cape Town in three decades made landfall late on Tuesday before hurtling eastwards along what is known as South Africa's "Garden Route".

"Humanitarian support is being co-ordinated for an estimated 8,000 to 10,000 residents of the greater Knysna area, after devastating fires last night," said James-Brent Styan, spokesman for the Western Cape local government ministry.

The bush wildfires, driven by winds in excess of 50km/h, destroyed property in 20 suburbs as buses were sent to evacuate trapped residents of the tourist town, renowned for its oysters and rugged coastal scenery.

According to the South African Weather Service, 37mm of rain fell at Cape Town airport. Other areas recorded as much as 131mm of rain.

Thousands of people in shantytowns, who have had to cope with the region's worst drought in a century, have been hardest hit, as floods and heavy rain washed away homes built of planks and zinc sheets.