King Haakon, Crown Princess Ingrid Alexandra, Dowager Queen Sonja and Prince Sverre Magnus are all attending the service, while Queen Mette-Marit is not attending as she is recovering from a lung transplant in June.
The church can accommodate 400 people and even before the doors opened at 10 a.m., long lines of mourners formed outside.
Several memorial services will be held throughout Norway on Sunday. Prime Minister Jonas Gahr Støre and several other representatives of Norwegian society will attend the service at Oslo Cathedral.
