Omicron cases have been confirmed in at least nine African countries, with some officials reporting that initial cases appear to be mild, while infections of the Delta variant surge across Europe.

Countries reporting Omicron include Botswana, Ghana, Mozambique, Namibia, Nigeria, Senegal, South Africa, Uganda and Zimbabwe.

South Africa remains the epicentre of the Omicron outbreak, with experts saying that the overwhelming majority of its thousands of new cases per day are of the new variant.

In east Africa, Uganda reported its first seven cases of omicron on Tuesday.

The variant was detected in travellers from South Africa and Nigeria who arrived at Entebbe International Airport on November 29 and are currently in isolation, the director of clinical services Charles Olaro said.

All of the travellers have mild symptoms, Minister of Health Jane Ruth Aceng said.

Five are from Nigeria and two came from South Africa, she said.

In southern Africa, Namibia has confirmed 18 cases of omicron, none of which are hospitalised, the country's health minister Kalumbi Shangula said.

Early evidence suggests that Omicron spreads faster but initially the symptoms appear to be mild, he said.

"Cases are going up but admissions are low," Shangula said of hospitalisations.

Omicron has quickly become the dominant variant in Namibia, he said.

"Omicron is a new variant, more is yet to be known about it, its behaviour and the effect that it will have on the pandemic trajectory," he said.

"The information available indicates current vaccines are still effective in reducing severe illness, hospitalisation and death."

Nigeria on Tuesday confirmed three additional cases of Omicron, increasing the number of confirmed cases of the variant in the west African country to six, according to the Nigeria Centre for Disease Control.

Meanwhile, the World Health Organisation said that by the end of this week, one in 10 people across the European Region will have had a COVID-19 infection, confirmed by laboratory testing.

The number of new infections and deaths has more than doubled in the past two months, WHO Regional Director Hans Kluge told an online press conference broadcast on Tuesday.

"The mortality would have been far worse without vaccination."

The WHO counts 53 countries in the European region including Russia and Turkey.

There have been nearly 90 million infections in the region and almost 1.6 million related deaths, according to WHO figures.

Kluge said the number of new cases was increasing in all age groups, with the highest numbers currently observed in the 5 to 14-year-old group.

There were 432 confirmed infections with the Omicron variant in a total of 21 countries in the region by Monday, he said.

"Omicron is in sight and on the rise and we are right to be concerned and cautious," he said.

The Delta variant of the coronavirus is the current problem and continues to dominate, he said.

"However we succeed against Delta today (and that) is a win over Omicron tomorrow."