The World Health Organisation has urged people to cancel some of their holiday plans to protect public health, as the Omicron variant gains ground around the world.

"An event cancelled is better than a life cancelled," said WHO head Dr Tedros Adhanom Ghebreyesus, adding that "difficult decisions" must be made.

Ghebreyesus warned that holiday festivities would lead to increased cases and more deaths in many places. WHO said it would be 'unwise' to conclude that Omicron was a milder variant than previous ones.

It said countries must prioritise many vulnerable people still waiting for a first vaccine dose.

Several countries have imposed stricter guidelines and rules for travel to halt the spread of the variant.

In the US, Omicron is now dominant, accounting for 73 per cent of new infections.

Americans are now advised against travel to more than 80 countries that appear on the Centers for Disease Control and Prevention's Very High list for Covid-19, including almost all of Europe.

France and Germany are among the nations imposing travel curbs to tackle Omicron, while the Netherlands has introduced a strict lockdown over the Christmas period.