Princess Astrid of Norway, the sister of the late King Harald V, has died at the age of 94, two days after attending his funeral, the country's royal palace has announced.

The new king, Haakon VIII, said that "throughout her long life, Princess Astrid represented the Royal House in a warm and dutiful manner".

Harald died last month, aged 89, after more than 35 years as king. His funeral was Astrid's last public engagement.

The princess will be buried at state expense and flags will be flown at half-mast across Norway, Prime Minister Jonas Gahr Støre said.

Astrid was the last surviving child of King Olav V, who reigned from 1957 to 1991.

She became Norway's first lady at the age of 22 in 1954, after the death of her mother Crown Princess Märtha. Olav did not remarry and Astrid retained the title until her brother's marriage in 1968.

"In her work, Princess Astrid was always particularly concerned with care and inclusion for the most vulnerable in society," her nephew King Haakon said in his statement.

Her health had deteriorated in recent months and in March she received hospital treatment for pneumonia.

Dozens of European royals and heads of state attended Harald's funeral on Wednesday, including the Prince of Wales and three Nordic kings.

Thousands of people lined the route during a procession from the royal palace to Oslo Cathedral on Wednesday afternoon.

The non-royal leaders paying their respects included Ukrainian President Volodymyr Zelensky, German President Frank-Walter Steinmeier and five foreign prime ministers.

In the final months of Harald's life, Norway's royal family faced personal challenges and scandal.

Earlier this year, documents revealed that King Haakon's wife, Queen Mette-Marit, had had frequent contact with US sex offender Jeffrey Epstein. She later said she wished she had never met the late disgraced financier.

Meanwhile, her son from a previous relationship, Marius Borg Høiby - who is not a royal but grew up within the family - was given a four-year jail term for two counts of rape in June.

Høiby, who is under house arrest pending appeal, was granted permission to attend the funeral.