Norway's King Harald has died aged 89, the palace said on Friday, his 53-year-old son Crown Prince Haakon automatically succeeding him on the throne.

"It is with deep sadness that we announce that His Majesty King Harald passed away today. King Harald passed away peacefully at Oslo University Hospital on Friday, August 28 at 6.35am," it said in a statement.

The flag at the royal palace in Oslo was lowered to half-mast.

Europe's oldest reigning monarch, King Harald had been in hospital in Oslo since August 17 suffering from haemolytic anaemia, a condition caused by an abnormally rapid destruction of red blood cells that leads to fatigue and shortness of breath.

The royal family had rushed to his bedside on Thursday as the palace announced that Harald's condition was "extremely serious".

His wife Queen Sonja, Haakon and his wife Mette-Marit and their adult children spent much of Thursday at his bedside, with media reporting that Haakon kept vigil overnight.

The public streamed to the palace in central Oslo for a second straight day on Friday, laying flowers on the ground and huddling in groups.

Kaspara Bolstad, 24, said Harald had been "a very steady and warm king".

"I think the entire Norwegian people see him as a role model and as someone who brings people together. Whether you're for or against the monarchy, I think he's well-liked across the board," she said.

Magnus Skaugseth, 27, agreed.

"He was so inclusive and committed to having values that are inclusive in the society we live in today. When there is so much division and polarisation, he was a pillar pointing in the opposite direction."

Harald, who ascended the Norwegian throne in 1991, had had multiple health problems in recent years, forcing him to have a pacemaker fitted and to scale back his official schedule.

But he always ruled out abdicating, arguing that he took a lifelong oath before the Norwegian parliament.

Norwegian Prime Minister Jonas Gahr Store cancelled a work trip to Germany early on Thursday due to the king's worsening condition. (AFP)


Edited by Aaron Tam