UK Health Secretary Sajid Javid said there were concerns the new variant "may be more transmissible" than the delta strain, and "the vaccines that we currently have may be less effective" against it.
Also, the European Union said Saturday it plans to stop air travel from southern Africa because of the variant as the 27-nation bloc is battling a massive spike in cases.
Irish golfer Paul Dunne told RTE Radio he was unaware of the situation at the Joburg Open when he finished out his delayed first round Friday. He has withdrawn and planned to take a flight to Dubai on Saturday.
"I'd three holes to finish in my first round, and when I came in I turned my phone on and I had messages from everyone asking me if I was going to go to the airport or stay and play. That's when I started to look into it," Dunne told the radio show.
"A few people are on the course without kind of a real idea of what's going on," he added, "but some people are finding it hard. I've heard people can't get a flight until Sunday evening."
Dunne said there were flights available but routing through Ethiopia, where fighting in the country's yearlong war draws closer to the capital, Addis Ababa.
"Bit of a minefield at the minute," he said.
Not every British player left. Ashley Chesters shot 2-under 69 on Friday to complete his second round on 7-under overall.
The Joburg Open is the start of a South Africa swing, followed by the SA Open and Alfred Dunhill Championship.
With the United Rugby Championship on hold in South Africa, Scarlets said in a statement it "would like to assure families and friends that we are making every effort to get our touring party back home to the UK as soon as possible."
Cardiff said "we are now looking to repatriate our staff ASAP."
Irish province Munster and Italian club Zebre Parma were also in South Africa.
Munster on Friday tweeted: "We all are safe & well in Pretoria. We are working with URC on the ongoing situation relating to Covid-19 & will provide an update once we know more."
Zimbabwe is hosting a qualifying tournament for the Women's Cricket World Cup in 2022. The eight visiting teams are the United States, West Indies, Netherlands, Ireland, Thailand, Sri Lanka, Bangladesh and Pakistan. Games were played this week and are scheduled through next week.
Warren Deutrom, chief executive of Cricket Ireland, said they are "very concerned about the latest developments" and have been in contact with the ICC, the Irish government and local officials "to better understand the facts, and to properly inform and reassure" the delegation.
"Our decision-making will be first and foremost based on the health and safety of players and support staff," Deutrom said in a statement on Friday. "We will provide updates as soon as we can."
