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 6:35 am," (0435 GMT) it said in a statement.
The flag at the royal palace in Oslo was lowered to half-mast, an AFP reporter at the scene said.
A few dozen people had gathered outside the palace in the morning, but after the flag was lowered to half-mast hundreds began making their way to the palace courtyard.
Hundreds of flowers had already been laid down the day before.
"Of course it's sad. He's a symbol of our country. And naturally, it's sad when something so beautiful comes to an end," 36-year-old Maja Otvik told AFP in front of the palace.
- 'Deep sorrow' -
Prime Minister Jonas Gahr Store said in a statement that he had received the news with "deep sorrow".
"An entire nation mourns, and at the same time remains profoundly grateful for a long life devoted to Norway," the head of government said.
"King Harald loved Norway. And Norway loved its king," he added.
The prime minister said the government would convene a conference "shortly" and thereafter meet the new king, Haakon, at the palace.
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 which 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.
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 had cancelled a work trip to Germany early Thursday due to the king's deteriorating condition.
The past year has been a turbulent one for the Norwegian royal family.
In February, King Harald was hospitalized for an infection and dehydration in Tenerife, where he was on a private trip with Queen Sonja.
His wife, also 89, was briefly admitted to hospital in May due to heart problems.
Haakon's wife Mette-Marit is under scrutiny for her ties to the late US sex offender Jeffrey Epstein.
Documents published in January in the United States revealed her sustained and at times intimate correspondence with Epstein between 2011 and 2014, at a time when the American financier had already been convicted.
Mette-Marit's son from a relationship prior to her marriage to Haakon, Marius Borg Hoiby, is also in the spotlight as a result of his legal troubles.
He was sentenced in June to four years in prison for two rapes and 32 other charges, including violence against a former partner. He has appealed the verdict.
Suffering herself from a serious lung disease, Mette-Marit, 53, had to undergo a lung transplant in July.
The royals remain broadly popular with the Norwegian public, in large part to Harald's unifying status and his unassuming, modest lifestyle.
