Torrential rains and freezing temperatures struck the largely rural and underdeveloped Eastern Cape on Monday, causing major flooding and landslides that submerged houses.

Images on local media showed homes completely under water and rescuers wading through the mud. Power and water supplies have been affected and hundreds have been forced to relocate.

"As the water subsides, more bodies are being discovered," said Caroline Gallant, Eastern Cape manager at the South African Red Cross Society, which has sent assistance to the disaster zone.

More than 3,000 houses have been affected, she told AFP, adding it was "the worst ever disaster" recorded in the area.

President Cyril Ramaphosa called the floods "unprecedented" and said he would visit the disaster-hit region Friday.

A previous death toll of 49 has now risen to 57, Velenkosini Hlabisa, minister of cooperative governance and traditional affairs, said.

"The figures are growing. This (57) is the figure... for the entire Eastern Cape province in three different areas," he told reporters, while visiting the worst hit city, Mthatha, about 800 kilometres (500 miles) south of Johannesburg.

Among the dead are at least four children who were in a school van that was swept away by the rising water, the province's top official Lubabalo Oscar Mabuyane has said.

Four other children are missing, while three were found alive. Two adults with them on the bus also died.

Another child died separately when he was swept away by water while walking to school, Basic Education Minister Siviwe Gwarube said early Thursday.

"We are reeling," she told public broadcaster SABC News.

- Door to door -

One rescuer, who spoke to AFP on Thursday on the condition of anonymity as he was not allowed to speak to the media, said his team was expecting to find more bodies and possibly survivors.

"We are going door to door to see, because yesterday we did find people locked inside houses who couldn't get out and were deceased," he said.

At least 600 people have been displaced, the provincial government said, with many sheltering in community halls.

Infrastructure has also been damaged and at least 20 health facilities affected, the local authority said.

"The numbers will increase dramatically," said Ali Sablay, a spokesperson for the Gift of the Givers Foundation, a disaster response charity that deployed teams to the area.

"In the last 24 hours the number of people requiring assistance has jumped from 5,000 to 10,000," he told AFP.

"The homes are fragile, they can collapse any time; food is contaminated so people need to be evacuated," he added.

The government urged South Africans to be vigilant over the next few days as more "extreme weather" was expected across the country.

The province -- where Nelson Mandela was born -- is among the poorest in the country, with 72 percent of people living below the poverty line, according to the Southern African Regional Poverty Network.

Snow and heavy rainfall are common during winter in South Africa but the country is also highly vulnerable to the impact of climate variability and change, which increases the frequency and severity of droughts, floods and wildfires, according to the Green Climate Fund.

"We must take a tough stance that everyone who is living on a flood plain must be removed," Hlabisa, the minister, said. "Climate change is a reality now."