At least 17 people died in the Eastern Cape and Gauteng, traffic was disrupted and two men were trapped on a mountain in Tuesday's icy weather.
In the Eastern Cape, rescuers were trying late on Tuesday afternoon to get to six people trapped in the Katberg Mountains.
Police disaster management co-ordinator Captain John Fobian said two people were initially stuck in the snow while trying to repair cellphone or telephone infrastructure. Their colleagues tried to help them and also got stuck.
"Now we're sitting with six people there, not two," said Fobian.
Police, military and Lukhanji municipal rescue teams were trying to reach them. A helicopter could not be used due to the weather.
Fobian said 13 people were known to have died from exposure in the province - four in Port Elizabeth, two in East London, two in Zwelitsha, two in Cofimvaba, two in villages near King William's Town and one in Dimbaza.
Fobian said more bad weather was forecast for the Eastern Cape. "Look for shelter."
In Gauteng, four people were reported dead, apparently in accidents while trying to keep warm.
In Nancefield in Soweto, two babies died when the shack they were in caught fire.
Johannesburg emergency services spokesman Malcolm Midgley said one was about four weeks old and the other about a year old.
The babies' mother left them alone in the shack while she went to fetch water and returned to find it in flames.
Midgley said the fire was believed to have been caused by illegal electrical connections to a hotplate.
In Sandton, a man died and another was taken to hospital in a "very serious" condition when they were overcome by the fumes from a brazier fire.
Midgley said the men were believed to be construction workers trying to keep warm overnight. "They took the brazier into the building, and sealed up all the doors and windows."
In Pretoria, a woman died after a fire gutted the Arcadia old age home just after midnight on Tuesday morning, said Tshwane emergency services.
"The elderly woman was burned to death when the Huiskroondal old age home caught fire," said spokesman Johan Pieterse.
He said 20 other elderly people rescued from the fire were treated for smoke inhalation. The cause of the fire was unknown.
The SA Weather Service recorded 54 weather records on Monday and Tuesday, almost all for the lowest maximum and minimum daily temperatures in towns across the country.
The lowest minimum temperature recorded was minus six degrees Celsius in Welkom, while the lowest maximum temperature was 1.7°C in Barkly East, both on Monday night.
None of this week's records reached the lowest temperature ever recorded in the country - -18.6°C at Buffelsfontein in the Eastern Cape mountains on June 28, 1996.
Weather SA said there was snow over the southern Cape and Eastern Cape high grounds, and the southern Drakensberg, and heavy rains along the south and south-east coasts and adjacent interiors.
"With the dry and cold air in circulation over the interior, this resulted in very low overnight temperatures."
Weather SA's Eastern Cape regional manager, Hugh van Niekerk, said there was snow on the Bamboesberge, at Joubertina, on the Tsitsikamma and Kouga mountains, at Hogsback, on the Outeniquas and Winterberg mountains, in the Barkly East and Molteno area, at Graaff-Reinet and Middelburg.
Weather SA warned that "very cold conditions are expected to persist over the southern highveld of Gauteng and Mpumalanga, Free State, Drakensberg mountains, and the interior of the Eastern Cape province as well as south-eastern part of Northern Cape".
Near Graaff-Reinet, 45 bus passengers spent a chilly night stuck in the snow on the Lootsberg pass on the N9 in a City to City bus.
Captain Erris Claassen said the bus got stuck about 6pm on Monday when the driver tried to get through the pass despite it being closed due to snow.
The passengers were rescued on Tuesday.
Twelve trucks were stuck in the pass and 10 were moved by the end of the day.
No injuries were reported.
"There are information signs just outside Middelburg as well as outside Graaff-Reinet to say the pass is closed. The drivers just keep ignoring the signs," said Claassen.
Nobody was fined for ignored the "closed" notices.
Fobian said the Penhoek pass on the N6 between Queenstown and Aliwal North had reopened but four other passes were still closed due to snowfalls. They are the Lootsberg, the Wapadsberg, Barkly pass on the R58 between Elliot and Barkly East, and the Nico Malan pass on the R351 between Seymour and Cathcart.
The N2 near Kokstad was closed on Tuesday morning after heavy snowfalls overnight, said KwaZulu-Natal transport department spokesperson Nonkululeko Mbatha.
The area closed was the Brooks Nek pass.
There were also reports of snow in Vryheid and Hlobane. - Sapa