Norwegian health authorities have said that three health workers who had recently received the AstraZeneca vaccine are being treated in hospital for bleeding, blood clots and a low count of blood platelets.
Norway halted the roll-out of the AstraZeneca vaccine on Thursday, following a similar move by Denmark. Iceland later followed suit.
"We do not know if the cases are linked to the vaccine," Sigurd Hortemo, a senior doctor at the Norwegian Medicines Agency told a news conference held jointly with the Norwegian Institute of Public Health.
All three individuals are under the age of 50.
The European medicine regulator, the European Medicines Agency (EMA,) would investigate the three incidents, Mr Hortemo said.
"They have very unusual symptoms: bleeding, blood clots and a low count of blood platelets," Steinar Madsen, Medical Director at the Norwegian Medicines Agency told broadcaster NRK.
"They are quite sick ... We take this very seriously," he said, adding that authorities had received notification of the cases yesterday.