Two people in the UK have been found to be infected with the new Covid-19 variant, Omicron, the UK government announced on Saturday as it added four more African countries to its travel red list.

Health Secretary Sajid Javid said the UK Health Security Agency (UKHSA) had detected cases in Chelmsford, Essex and in Nottingham.

The cases are said to be linked and the two people were self-isolating alongside their households while more tests and contact tracing take place.

Also, the government said four more countries are being added to the travel ban red list from 4 AM on Sunday: Angola, Mozambique, Malawi and Zambia.

This adds to the six countries on the ban list since Friday South Africa, Botswana, Lesotho, Eswatini, Zimbabwe and Namibia.

"We've always been very clear that we won't hesitate to take further action if that is what is required," said Javid.

"Today I can announce one thing that we are doing immediately is carrying out targeted testing and sequencing of positive cases in the two areas that are affected. This is a real reminder that this pandemic is far from over. If there is one thing that everyone can be doing, right now, is if they are eligible, please take your vaccine, whether it's your first shot, second shot, or your booster jab," Javid said.

Omicron was on Friday declared by the World Health Organisation (WHO) a variant of concern, putting it in the same category as the Delta variant, which has caused waves of infection to sweep across the globe and forcing several European countries to re-enter lockdown.

The new variant is considered potentially more dangerous because it has around twice as many mutations as Delta, but experts say how much of a concern is still under investigation.

Omicron, also called B.1.1.529, has also been detected in Belgium, Israel and Hong Kong, and possibly in Germany and the Czech Republic.

UK officials insist that the reason two cases had been detected in the UK now was as much because the UK is a world leader in genomic sequencing.

Javid said on Twitter that as a precaution we are rolling out additional targeted testing in the affected areas - Nottingham and Chelmsford - and sequencing all positive cases. This is a fast-moving situation and we are taking decisive steps to protect public health.

We are also adding Malawi, Mozambique, Zambia and Angola to the travel red list - effective from 4am Sunday. If you have returned from there in the last 10 days you must isolate and get PCR tests. And if you are eligible for your booster jab - now is the time to get it, Javid tweeted.

The new potentially more contagious was on Friday designated as a Variant of Concern by the WHO, which named it Omicron. A variant of concern is the WHO's top category of worrying Covid-19 variants.

The variant has a high number of mutations, about 50 overall.

Crucially, South African genomic scientists said Thursday more than 30 of the mutations were found in the spike protein -- the structure the virus uses to get into the cells they attack.

Countries around the world are currently racing to introduce travel bans and restrictions on southern African countries in an effort to contain Omicron's spread.

The US has from Monday restricted travel from South Africa and seven other countries in the southern Africa region.

European countries along with the UK have banned travel to and from South Africa and neighbouring countries of Namibia, Zimbabwe and Botswana, as well as Lesotho and Eswatini (formerly Swaziland), both of which are landlocked within South Africa.

Other countries include Mauritius, Israel, Sri Lanka and the Netherlands.

Many other countries followed suit, most of them indicating that only their own citizens would be allowed back, subject to a quarantine period.

In New Delhi, the Indian government asked all states and union territories to conduct rigorous screening and testing of all international travellers coming from or transiting through South Africa, Hong Kong and Botswana, where a new variant has been detected.

PTI