South African President Cyril Ramaphosa is being treated for mild COVID-19 symptoms after testing positive for the disease, his office says.

Mr Ramaphosa started feeling unwell and a test confirmed the presence of the virus, a statement from the presidency announced on Sunday (local time).

The statement did not say whether he had been infected with the Omicron variant.

Mr Ramaphosa is self-isolating in Cape Town and is being monitored by the South African Military Health Service, the statement said.

He has delegated all responsibilities to Deputy President David Mabuza for the next week.

Mr Ramaphosa, 69, is fully vaccinated.

Last week, he visited four West African nations. He and all members of his delegation were tested for COVID-19 in each of the countries during the trip.

Some in the delegation tested positive in Nigeria and returned directly to South Africa. Throughout the rest of the trip, Mr Ramaphosa and his delegation tested negative. Mr Ramaphosa returned from Senegal on December 8.

Mr Ramaphosa said his own infection served as a caution to everyone in South Africa to be vaccinated and remain vigilant against exposure, the statement said.

South Africa is battling a rapid resurgence in virus cases, driven by the Omicron variant.

The country had more than 18,000 confirmed cases on Sunday night. More than 70 per cent of those are estimated to be Omicron, according to genetic sequencing.

After a period of low transmission of about 200 cases a day in early November, South Africa’s COVID-19 cases began rising dramatically.

On November 25, scientists in southern Africa confirmed the presence of the Omicron variant, which has more than 50 mutations.

Omicron appears to be highly transmissible and has quickly become dominant in the country.

So far, the majority of cases have been relatively mild and the percentage of severe cases needing oxygen have been low, doctors say.

-AAP