CNN) -- An explosion has rocked a French oil tanker, ripping a hole in the hull above the waterline as it was being cleaned in the Atlantic Ocean off Bayonne, French authorities said.

The explosion occurred at 7:15 a.m. local time Friday (0545 GMT) on the "Chassiron," a 10,000-ton tanker anchored in the Landes region waters. One crew member from the 14-member crew was missing.

The tanker's oil tank was empty, the Atlantic Prefet and the Regional Center for Surveillance and Security said, adding the explosion was believed to be an accident. Authorities said they were excluding terrorism as the cause.

They said the explosion happened during cleaning at the stern of the ship. Part of the bridge was damaged and the hull was breached above the water line.

The Chassiron is 119 meters long and was built in 1999.

Rescue officials from Bayonne and Anglet, France as well as Bilbao, Spain rushed to the scene.

The explosion is under a judiciary investigation opened by the Bayonne public prosecutors department and the National Maritime Police.