Up to 70% of sampled Covid-19 cases in the last month were as a result of the Omicron variant of the coronavirus.

In a digital briefing on Friday, Health Minister Joe Phaahla said Omicron was fast becoming the dominant variant in South Africa, overtaking the Delta variant.

Omicron has now been identified in 57 countries around the world.

He added that the reproductive number of the virus (the number of people who are likely to be infected by one person) was 2.5 - higher than it was at any other point in the pandemic.

"Omicron has driven the resurgence in South Africa," Phaahla said.

He added that 90 000 cases had been reported in all provinces in just under a month. On Thursday, there were more than 22 000 new infections.

He also said that 70 % of the samples sequenced since November, showed Omicron as the dominant variant. 

Phaahla added that so far, it appeared that patients who were admitted to hospital during the fourth Covid-19 wave experienced a less severe form of the disease.

He said, "Scientists have been conducting rapid research to better understand many aspects of the Omicron variant, including how well this variant transmits and whether it can escape some of our immunity."

The National Institute for Communicable Diseases' (NICD) Michelle Groome said during the briefing that the country's seven-day moving average was more than 13 000. This was being driven primarily by increased cases in Gauteng, especially among younger age groups.

"We've seen a dramatic increase - much higher than in the second or third waves," she said.

She added that there were slight increases in the hospitalisation rate, primarily due to admissions in Gauteng.

Dr Mathabo Mathebula, CEO of Pretoria's Steve Biko Academic Hospital, said hospital admissions appeared to be for age groups where there was lower vaccine coverage.

However, she said, there were early indications that fewer patients require oxygen or ventilation once hospitalised. The length of hospital stays has also shortened.

However, Groome cautioned that due to the sharp increase in cases, hospitalisations could increase over the next few weeks and result in different data.