A "sustained increase" in Covid-19 cases in Gauteng has been driven by a cluster outbreak among students at the Tshwane University of Technology in Pretoria.

In a statement, City of Tshwane spokesperson Sipho Stuurman said the city has "recorded a sharp increase in the number of active Covid-19 cases".

He said there were 1 689 active cases in the city on Monday - an increase from 362 the previous week.

New confirmed daily cases have also increased exponentially from below 50 to above 300. On Monday, there were 383 new cases.

"Other areas of concern with increased infections include Hatfield, Atteridgeville, Mamelodi East, Centurion and Soshanguve," Stuurman said.

On Monday, the National Institute for Communicable Diseases (NICD) flagged an increase in the seven-day moving average in new Covid-19 cases in Gauteng.

The increase appears to be in Pretoria, in the age group 10 to 29.

"Additionally, the NICD has recently identified a cluster among the 20 to 44 age group at an institute of higher education in Tshwane," said NICD acting executive director Professor Adrian Puren.

He added, "We are monitoring these trends to see if these increases persist. Localised increases in case numbers (clusters) are not unexpected. However, it is hard to say whether the increases indicate the start of a widespread resurgence."

On Monday, Gauteng accounted for 77% of South Africa's new cases, with 239 new infections.

The NICD said 312 new Covid-19 cases were reported, bringing the total number of laboratory-confirmed cases in the country to 2 930 174. The increase represented a 2.3% positivity rate.