Countries tighten restrictions over new COVID strains

This new variant is "yet more transmissible" and the development is "highly concerning," he said.

The cases and close contacts of the cases found in Britain are being quarantined, and the British government is placing "immediate restrictions" on travel from South Africa, according to Hancock.

Meanwhile, another new variant of the coronavirus appears to have emerged in Nigeria, the Africa Centres for Disease Control and Prevention (Africa CDC) said Thursday.

"It's a separate lineage from the UK and South Africa," John Nkengasong, head of the Africa CDC, told reporters, adding more investigations are needed.

So far, the new variants have been detected in Australia, Denmark, Italy, Iceland, the Netherlands, Germany, Canada and Japan, according to the World Health Organization (WHO) and media reports.