By Gwladys Fouche and Nerijus Adomaitis
OSLO (Reuters) -Norway is reintroducing some nationwide restrictions to curb the spread of COVID-19 following the emergence of the new Omicron variant, the government said on Thursday, as a fifth case of the latter was confirmed and more expected.
From midnight local time (2300 GMT), all travelers arriving to Norway, both vaccinated and unvaccinated, must take a test within 24 hours of arrival.
In areas with high infection rates, such as the capital Oslo, the use of face masks in crowded places will be mandatory, as will working from home, at least for part of the week, for those who are able to.
The measures were taken after a fifth person tested positive for the Omicron variant on Thursday in the wake of a corporate Christmas party in Oslo last week, but Prime Minister Jonas Gahr Stoere said the exact number was likely higher.
"Since Tuesday we have had a big outbreak of the Omicron variant in Oslo. Over 50 people have been infected at an event. All of these were fully vaccinated," Stoere told a news conference.
The Norwegian Institute of Public Health said it was trying to determine how many of the over 50 COVID-19 cases from that party involved the Omicron variant.
"We know that they have been infected with the coronavirus, but we don't know which variants yet. We will know that in a couple of days," said an institute spokesperson.
Underlining the potential challenges posed by Omicron, authorities said there had been no issues with the way the company Christmas party was organised.
"The people at the Christmas party did everything right. They were vaccinated. They took a test ahead of the party," the governing mayor of Oslo, Raymond Johansen, told a news conference.
Norway posted a single-day record of 4,624 coronavirus cases on Monday, according to data from the Norwegian Institute of Public Health.
On Tuesday https://www.reuters.com/business/healthcare-pharmaceuticals/norwegians-should-wear-face-masks-crowded-places-pm-says-2021-11-30, Stoere urged Norwegians the wearing of face masks in crowded places and the speeding up of booster vaccinations in the hope of avoiding a new lockdown. He had stopped short of issuing mask mandates, which were urged by some municipalities.
Some 88% of adults in Norway, and 71% of all Norwegians, are fully vaccinated. About 11% have received a booster shot.
(Editing by Nick Macfie and Bernadette Baum)