Norway has announced new restrictions to contain COVID-19 in Oslo and the surrounding region after an outbreak of infections linked to a Christmas party.

More than half of some 120 people present have tested positive -- even though they were reportedly all vaccinated -- and it's feared many may have contracted the Omicron variant.

If confirmed, it would be the biggest single outbreak of the variant in Europe.

The cases are connected to a Norwegian company’s Christmas party in an Oslo restaurant, officials said on Thursday. All those who attended the event were tested after the dinner, organised by the solar energy company Scatec in an Oslo restaurant last Friday (November 26).

"The situation is worrying," said Norway's health minister Ingvild Kjerkol, shortly after Oslo health authorities said that one Omicron infection had been confirmed from the company event.

"This shows that the virus spreads very easily and that the vaccine does not protect well against infections. We hope and believe that the vaccine protects against serious forms of the disease but we don't know up to what point," Kjerkol added.

New restrictions from Friday

Wth much remaining unknown about the new variant, the Norwegian government said new national and regional restrictions would take effect from Friday. Norwegian Prime Minister Jonas Gahr Stoere the strictest measures were regional and would apply to Oslo — a city of nearly 700,000 — and surrounding districts.

He said they include working from home when possible, a 100-person attendance limit at private indoor events in public places or rented venues, and restaurants and bars having to register customers.

Nationally, anyone entering Norway must be tested within 24 hours, either at the border, at a public test station or by self-test. If a rapid test comes back positive, a traveller must take a PCR test within 24 hours, the government said.

”It is likely that the Omicron variant will spread in Norway, and that is why the government believes in stricter measures," Gahr Stoere said.

On Tuesday, Norway recommended the use of face masks on public transportation and in shops and shopping malls.

“We still have to keep our distance to get control of the spread of infection, but that does not mean that we cannot have good contact with each other,” Gahr Stoere said.