The royal couple, both 83, are said to both be feeling well and are presenting no symptoms of the virus. They will undergo testing and a further statement will be made when those results are in.
In addition to King Harald and Queen Sonja, 14 employees at the Royal Court are also now in quarantine.
WATCH: Royals wearing face coverings
King Harald was tested for coronavirus back in October, which came back negative, ahead of an operation to replace a heart valve after he began suffering breathing difficulties.
Following the procedure, the monarch's doctor Bjoern Bendz from Rikshospitalet's Cardiovascular and Lung Clinic, said: "The king is in good shape."
The royal couple are in voluntary isolation
While King Harald and Queen Sonja are expected to continue their work from isolation as much as is possible, Haakon Magnus, His Royal Highness the Crown Prince, 47, will take over his father's role with the President of Estonia at a planned event on 20 November.
This is not the first time the couple has had to isolate. Following a royal visit to Jordan in March, they were confined to their home for a period of self-isolation.
It is expected a new statement will be released with their test results
King Harald issued a statement at the time, which read: "Our country is in a serious situation that affects individuals and society as a whole.
"It is crucial that we all participate in the national quest to avoid exposing ourselves or others to infection. It is therefore important that we all follow recommendations and orders from the authorities.
"We must contribute what we can to prevent the spread of the virus, and I would especially like to thank health professionals all over the country who are doing their utmost to remedy the situation these days. We all hope that developments will soon turn around."
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