Flights resumed at the airport after military troops piled sandbags around the 250-kilogram (550-pound) bomb all through the night. The airport was closed all day Tuesday, with 92 flights in and out cancelled, the Associated Press reported.
The rust-covered bomb has been identified as made in the U.S.
The airport was a Japanese military flight school during the war, the BBC reported. It was closed for months due to damage from the earthquake and tsunami that hit Japan in March last year. The bomb was uncovered when parts of the airport were being restored.
It could take a week to dispose off the bomb, which the officials plan to transport elsewhere or ready it for a controlled detonation on site, the Associated Press reported.
Uncovering of bombs from World War II is not rare in Japan, especially in the southern island of Okinawa and even Tokyo.
Okinawa was one of the worst affected in the Pacific war, with U.S. forces pounding the region for 83 days resulting in the death of some 190,000 Japanese, half of them Okinawan civilians.
In July 2010, as many as 902 unexploded munitions — including rocket bombs, grenades and motor projectiles — believed to have been made in the U.S. were unearthed in Itoman city in Okinawa during a road expansion project.
Last week, hundreds of residents in central Tokyo were evacuated after a 220-kilogram dud was found buried there.
An estimated 10,000 tons of unexploded munitions were left in Okinawa after the war. About 4,500 tons remained by the time the U.S. returned Okinawa to Japan in 1972, according to the Daily Telegraph.