Updated

Navy officials said Wednesday night they're investigating a possible fuel leak in a tank at an underground facility built in Hawaii in the 1940s.

Navy officials said fuel operators found a discrepancy in the tank's levels on Monday. Manual measurements showed the tank possibly lost fuel, the Navy said.

Navy spokesman Tom Clements said it's not clear whether any aviation fuel was truly lost because measurements would take several days to complete. He said he did not know how much fuel was in the tank, though the 200-foot tall cylinder holds 12.6 million gallons.

When operators found the measurement discrepancy, they began transferring fuel immediately to another tank, a process that could take up to five days, Navy officials said.

The Navy said it informed state and local officials, and nearby wells were closed as a precaution. Local water officials were investigating separately, the Navy said.

The Red Hill Underground Fuel Storage Facility held fuel for American planes in World War II. It has 20 total tanks that have capacity to store a total of 252 million gallons, buried about 100 feet underground. The inland facility is about two miles north of Pearl Harbor, near a state prison and just east of a freeway that connects Honolulu with the suburb of Kaneohe on Oahu's windward coast.

The Navy started building the facility in 1940, less than one year before the Dec. 7, 1941 attack on Pearl Harbor that propelled the United States into World War II. It was built to protect fuel from being destroyed above ground.

Navy officials said the tank held JP-8 aviation fuel, made of mostly kerosene.