A nuclear power plant in northern France hit by a jellyfish invasion was getting back online on Wednesday, operator EDF said, with service restored at the first of four closed reactors.

Four reactors at France's Gravelines nuclear plant will return to operation throughout the week, slightly later than initially planned, EDF data showed on Tuesday, after they were forced offline by a swarm of jellyfish in the cooling systems.

Located on the Channel coast near Dunkirk, Gravelines is the largest nuclear power plant in western Europe, with six 900 megawatt reactors.