South African President Cyril Ramaphosa on Sunday called on countries to "immediately and urgently" reverse scientifically "unjustified" travel bans linked to the discovery of the new coronavirus variant Omicron.

"We call upon all those countries that have imposed travel bans on our country and our southern African sister countries to immediately and urgently reverse their decisions," he said in his first address to the nation following last week's detection of the new variant.

Dozens of nations have blacklisted South Africa and its neighbours since South African scientists flagged Omicron on November 25.

The World Health Organization has labelled Omicron a variant of concern, while scientists are still assessing its virulence.

A "deeply disappointed" but calm-looking Ramaphosa said the "prohibition of travel is not informed by science."

The countries that have already imposed travel restrictions on southern Africa include key travel hub Qatar, the United States, Britain, Saudi Arabia, Kuwait and the Netherlands.

Ramaphosa's Malawian Lazarus Chakwera earlier Sunday accused Western countries of "Afrophobia" for shutting their borders. Ramaphosa warned that prohibition on travel would "further damage the economies (and) undermine their ability to respond to and recover from the pandemic".

South Africa, the continent's most industrialised economy, is struggling with slow growth and a more than 34 percent unemployment rate. The travel bans are another major blow to its tourist industry, which had set high hopes on the upcoming southern hemisphere summer.

Ramaphosa blasted the G20 countries for sidelining commitments made at a meeting in Rome last month to support the recovery of the tourism sector in developing countries.

"These restrictions are unjustified," he fumed with uncharacteristic vehemence. Ramaphosa called on rich countries to stop fuelling vaccine inequality, describing jabs as the "most powerful tool" to limit Omicron's transmission.

He made a fresh impassioned appeal to South Africans to get their shots and said the government was considering making vaccines mandatory for certain activities and locations in a bid to increase uptake.

"Vaccines do work. Vaccines are saving lives," he said. Just over 35 per cent of adults in South Africa have been fully inoculated after a slow start to the vaccine campaign, with vaccine hesitancy widespread.  

The country is Africa's worst-hit by Covid, with around 2.9 million cases and 89,797 deaths reported to date. Omicron is believed to be fuelling a rise in infections, with 1,600 new cases recorded on average in the past seven days compared to 500 the previous week.