Only vaccinated people were allowed into the event last Friday evening at an Oslo restaurant, with media reports saying roughly 120 people had been there.
“We have up to 50 who have tested positive with a PCR as well as about 10 with rapid tests,” city official Tine Ravlo told local media.
“So far, one person has been diagnosed with Omicron and more cases are expected,” Oslo municipality announced in a statement.
“Active tracing is under way to limit the possibility of contamination and prevent a larger outbreak.”
If the Omicron variant were to be detected in all of them, this would be one of the largest known outbreaks of the new variant in Europe.
And if all the diners were confirmed to have been vaccinated, it would raise questions about the effectiveness of the jabs against the new variant.
Another Oslo official Jorunn Thaulow added that the high proportion of positive tests was “an indication that this is a contagious variant, no doubt about it”.
Norway has extended the isolation period for people who have tested positive for the Omicron variant to seven days and increased the quarantine period for their relatives to 10 days.
The Scandinavian country, which has seen a recent rise in the number of Covid infections, hospitalisations and deaths, reported on Wednesday the first four cases of the Omicron variant.
Separately two cases of the Omicron Covid-19 variant were registered in Øygarden Municipality, western Norway, on Wednesday.
Mayor of Øygarden Municipality Tom Georg Indrevik said that the two people who tested positive for that variant had recently travelled from South Africa.
Indrevik added that the municipality had been in contact with health authorities and was taking the matter seriously.
“We have been in contact with the Norwegian Institute of Public Health (NIPH) over the weekend, and extra precautions have been taken with regard to those who are infected with the Omicron variant,” he said.
Shortly after the first two cases were reported, two probable cases were reported in Ullensaker, east Norway, which is the municipality where Oslo Airport Gardermoen is located.
The Norwegian Institute of Public Health (NIPH) said that preliminary analysis indicated that the infections were probably the Omicron variant.
“The people in question came by plane to Oslo Airport and have been in quarantine hotels at Gardermoen since arrival. They travelled from South Africa to Norway on two different planes between 26th and 28th November,” NIPH said in a statement.
Broadcaster TV2 reports that several municipalities have contacted NIPH due to suspected Omicron cases.
“There are a number of suspected cases that are being analysed now in various laboratories in the country,” NIPH department director Line Vold told TV2.
Director of Health at the Norwegian Directorate of Health, Bjørn Guldvog, said the detection of Omicron in Norway is to be expected.
“It is not surprising that we have now been able to detect the first cases of Omicron infection also in Norway. Together with the NIPH and the Ministry of Health and Care Services, we will now follow the situation closely in the future,” he told public broadcaster NRK.