The late king was a popular and reforming leader in Norway who modernised the monarchy.
He broke with tradition by marrying a commoner, Queen Sonja, and served as a unifying figure during Norway’s most difficult moments.
Harald died a day before their 58th wedding anniversary.
Members of the public have been gathering to lay flowers at a memorial outside the Royal Palace in Oslo.
Norway’s Prime Minister Jonas Gahr Støre said in a televised memorial address that his country was “united in grief and gratitude” for Harald’s service and that his “legacy lives on”.
The UK’s King Charles III said he was mourning his “dear cousin”. King Harald V was a second cousin of the King’s mother, Queen Elizabeth II.
Haakon VIII is the great-great-great-grandson of Queen Victoria.
