Asian countries rushed to tighten restrictions after a new and possibly vaccine-resistant coronavirus variant was detected in South Africa, with Singapore (above) and India announcing stricter border controls and more rigorous Covid-19 testing on Friday.

Scientists are still finding out more about the new variant, first identified at the start of this week, but the news pummeled financial markets on Friday, with stocks in Asia suffering their sharpest drop in three months and oil plunging more than 3%.

The variant, called B.1.1.529, has also been found in Botswana and Hong Kong...