Norway's King Harald V was admitted to Oslo University Hospital on Friday after suffering from breathing difficulties, but he does not have Covid-19, the royal palace said.
The king is being examined and on sick leave, the palace added.
His son, Crown Prince Haakon, chaired Friday's regular state council session with the Cabinet.
Prime Minister Erna Solberg said she hoped the king would have a speedy recovery. More well wishes came from Jonas Gahr Store, the opposition Labour party leader, news agency NTB reported.
Harald, aged 83, became king in 1991.
Queen Sonja visited the king on Friday, but left the hospital around 11 am in her own car, public broadcster NRK reported.
She was set to attend the opening of her childhood home - which has been moved to the Maihaugen open-air museum in Lillehammer, north of Oslo - later on Friday. The king was initially scheduled to accompany her to the ceremony.
Heart surgery and cancer
The king on Thursday attended a disembarkation ceremony marking the end of the season for the royal yacht "Norge," where he thanked the crew.
In December, Harald cancelled a few engagements due to a viral infection, but gave his annual New Year's speech as scheduled. In early January, he spent a week in hospital after suffering from dizziness.
The king underwent heart surgery in 2005 and at the end of 2003 was operated on for bladder cancer. Both procedures were described as successful.
In November 2017, the king was also briefly hospitalized for an infection.