Norway on Thursday recorded the highest number of new coronavirus infections since the start of the pandemic, with 1,294 positive cases.
In the past two weeks, there have been 152 reported cases per 100,000 residents, the health authority said.
Numbers have skyrocketed - specially in cities like Oslo, Bergen and Trondheim - after the end of the summer holidays.
At a school in Oslo, 79 people tested positive for the virus on Thursday.
Many places no longer have enough capacity to track down the sources of infection and the people who have been in contact with them.
"Many of those infected have many close contacts," Beate Husa, a health councillor in Bergen, told Norwegian broadcaster NRK.
Health authorities, however, said on Wednesday that the pandemic was under control despite the higher figures. The number of hospital admissions is rising, but still at a low level.
In Norway, around 62% of the adult population is fully vaccinated.