South Africa says the detection of Omicron has seen a sudden rise in COVID-19 infections within a short space of time.

President Cyril Ramaphosa said on Sunday night that the increase has been pronounced in Gauteng, although cases were also rising in other provinces.

"We have seen an average of 1,600 new cases in the last seven days, compared to just 500 new daily cases in the previous week, and 275 new daily cases the week before that," Ramaphosa said in a televised address to the nation on national efforts to contain the COVID-19 pandemic. "The proportion of COVID-19 tests that are positive has risen from around 2 percent to 9 percent in less than a week."

He warned the nation will likely experience a fourth wave by early December.

The Omicron variant was first detected in Botswana and South Africa, and later in many other countries including Australia, Belgium, Italy, the United Kingdom, Germany, Austria, Denmark and Israel.

President Ramaphosa said so far South African scientists had established that the Omicron has far more mutations than any previous variant; is readily detected by the current COVID-19 tests; is different from other circulating variants, and was responsible for most of the infections found in Gauteng over the last two weeks.

South Africa has administered over 25 million doses of vaccines since the inception of the vaccination program in May. Forty-one percent of the adult population have received at least one vaccine dose, and more than 35 percent of adult South Africans are fully vaccinated against COVID-19.

Ramaphosa said South Africa, like a number of other countries, is looking at booster vaccines for people who are at greatest risk and for whom a booster may be beneficial.

Despite the rise in infections, the South African Cabinet left COVID-19 restrictions on Alert Level 1 because a lot more people have been vaccinated and vaccines are available to anyone.

Alert Level 1 regulations impose a 12 midnight to 4 am curfew, and prohibits over 750 people to gather indoors and no more than 2,000 people to gather outdoors. Only 100 people are permitted at a funeral, and night vigils, after-funeral gatherings and 'after-tears' gatherings are not allowed.

Ramaphosa condemned countries that had unjustifiably banned travel from a number of Southern African countries following the identification of the Omicron variant.

"This is a clear and completely unjustified departure from the commitment that many of these countries made at the meeting of G20 countries in Rome last month.

"They pledged at that meeting to restart international travel in a safe and orderly manner, consistent with the work of relevant international organizations such as the World Health Organization," he said.