At least 49 people, including several schoolchildren, have been killed in the floods that have swept through South Africa's Eastern Cape province as torrential rain and snow have hit parts of the country.

"The numbers are just escalating hour after hour. The situation is so bad on the ground," provincial premier Oscar Mabuyane said.

Among the bodies recovered are those of four children, a driver and a conductor who were on a bus that was carried away in flood waters as it was crossing a bridge in the town of Mthatha on Tuesday morning.

Mabuyane said rescue efforts were continuing to find four more children who had been in the vehicle that had been found on a riverbank with no one inside.

Earlier, an official had told private TV station Newzroom Afrika that eight bodies, including that of the bus driver, had been found.

Public broadcaster SABC reported that three children were rescued alive on Tuesday, found clinging to trees.

It is now known that there were 13 people on the bus, 11 of them schoolchildren.

On Wednesday morning, Mr Mabuyane visited the scene to witness rescue efforts, and to meet affected communities in Decoligny, a village outside Mthatha.

Hundreds of residents had been left displaced, many spending the night in makeshift shelters, he said.

Mr Mabuyane praised those who were assisting officials in locating the missing and for alerting their neighbours when the floods began.

Officials said 58 schools in Eastern Cape had been affected across three districts: OR Tambo, Amathole and Alfred Nzo.

"For all these years that I've lived, I've never seen something like this," Mr Mabuyane said.

In neighbouring KwaZulu-Natal, 68 schools across nine districts have been damaged but no fatalities have been recorded.

The heavy snow, rains and gale force winds have also left nearly 500,000 homes without electricity since Tuesday - and state-owned power provider Eskom says efforts are being made to restore connections.

South Africa's President Cyril Ramaphosa has offered his condolences to the families of those who died as he urged citizens to "display caution, care and cooperation as the worst impacts of winter weather take effect across the country".

The Eastern Cape - the birthplace of anti-apartheid icon Nelson Mandela - has been worst-affected by the icy conditions, along with KwaZulu-Natal province.

The bad weather has forced the closure of some major roads in the two provinces to avoid further casualties.