A 60-year old Danish woman who died of a blood clot after receiving AstraZeneca's Covid-19 vaccine had "highly unusual" symptoms, according to the Danish Medicines Agency.

The woman had a low number of blood platelets and clots in small and large vessels, as well as bleeding, it said.

A few similar cases were found in Norway and in the European Medicines Agency's (EMA) database of drug side effects, Danish Medicines Agency said.

"It was an unusual course of illness around the death that made the Danish Medicines Agency react," it said in a statement late on Sunday.

Norway said on Saturday that three people, all under the age of 50, who had received the AstraZeneca vaccine were being treated in hospital for bleeding, blood clots and a low count of blood platelets, which were labeled "unusual symptoms" by health authorities.

Denmark, Norway and Iceland said last week they would halt the introduction of the AstraZeneca vaccine.

European vaccination programmes have been upset in the last two weeks by reports that recipients of the AstraZeneca inoculation have suffered blood clots.

The European Medicines Agency has said there is no indication that the events were caused by the vaccination, a view that was echoed by the World Health Organization on Friday.

AstraZeneca Plc said on Sunday a review of safety data of people vaccinated with its Covid-19 vaccine has shown no evidence of an increased risk of blood clots.