Greece has banned public Christmas and New Year's Eve festivities and mandated mask-wearing in open spaces to help to curb the spread of the Omicron coronavirus variant, its health minister says.

The measures will be in effect from Friday morning and will also require citizens to wear two masks or masks offering high protection on public transport and in supermarkets.

Foreign visitors are "strongly encouraged" to take two PCR tests a few days after arrival.

Health Minister Thanos Plevris said additional measures were expected in the new year, mainly in entertainment and sports events, to avoid another lockdown.

"We are constantly monitoring the cases to see if behind Delta variant there is a spread of Omicron," he told a news conference on Thursday.

Greece has reported only a few dozen of Omicron cases since the beginning of the month.

With the second Christmas of the pandemic a few days away, many countries have imposed new restrictions on their citizens while worrying about the damage the new variant might inflict on their economies.

Greece, which emerged from the first wave of the pandemic last year in relatively better shape than some other European countries, has been grappling with a surge in infections in recent months that have put a strain on its healthcare system.

Authorities reported 5641 new infections and 69 related deaths on Wednesday, bringing the total number of infections since the pandemic began to 1,049,936 and the death toll to 20,126.

With a population of 11 million people, Greece has so far administered more than 7.3 million first shots. About 65.7 per cent of Greeks are fully vaccinated.