At least 13 people in Oslo have been infected with the Omicron variant of the coronavirus following a corporate Christmas party described as a "super spreader event", and their numbers could rise to over 60 cases, authorities said on Friday.

The outbreak took place at a Christmas party on November 26 organised by renewable energy company Scatec, which has operations in South Africa where the variant was first detected.

"This party has been a super spreader event," Preben Aavitsland, a senior physician at the Norwegian Institute of Public Health, told Reuters by email.

"Our working hypothesis is that at least half of the 120 participants were infected with the Omicron variant during the party. This makes this, for now, the largest Omicron outbreak outside South Africa."

Aside from the people infected at the party, Aavitsland said, two people living on the country's west coast and two people in quarantine at Oslo airport have been confirmed as carrying the Omicron variant of the coronavirus.

The outbreak led the Norwegian government to reintroduce some nationwide restrictions to curb the spread of Covid-19.