"This discharge is understood to have occurred in connection with starting up production from the Tordis field, which is tied back to Gullfaks C," the Petroleum Safety Authority (PSA) said in a statement.

"Oil was observed on the sea after production had got under way. Gullfaks operator Equinor has estimated the size of the spill at 17.5 cubic metres (110.1 barrels) of oil," it added.

(Reporting by Terje Solsvik, editing by Nerijus Adomaitis)