Norway’s 89-year-old King Harald is in an “extremely serious” condition after his health deteriorated while he was being treated in a hospital in Oslo.

The king has been hospitalized since August 17 with haemolytic anaemia, a blood disorder that causes red blood cells to break down too quickly.

He also developed a bacterial infection in his blood and has been receiving treatment for the infection.

Queen Sonja and Crown Prince Haakon, who is serving as regent, canceled their public engagements and went to the hospital to be with him, Al-Jazeera has reported.

King Harald has ruled Norway since 1991 and is Europe’s oldest reigning monarch, with his worsening condition prompting widespread concern across the country.