An unexploded US bomb from World War II that had been buried at a Japanese airport has exploded, causing a large crater in a runway, Japanese officials say.

Land and Transport Ministry officials said there were no aircraft nearby when the bomb exploded at Miyazaki Airport in south-western Japan.

More than 80 flights were cancelled but there were no injuries.

Officials said an investigation by Japan’s Self-Defence Forces and police confirmed that the explosion was caused by a 225-kilogram US bomb and there was no further danger.

They were determining what caused its sudden detonation.

A video recorded by a nearby aviation school showed the blast spewing pieces of asphalt into the air like a fountain.

Videos broadcast on Japanese television showed a crater in the taxiway reportedly about seven metres in diameter and a metre deep.

Chief Cabinet Secretary Yoshimasa Hayashi said more than 80 flights had been cancelled at the airport, which hoped to resume operations on Thursday.

Miyazaki Airport was built in 1943 as a former Imperial Japanese Navy flight training field from which some kamikaze pilots took off on suicide attack missions.

Other unexploded bombs dropped by the US military during WWII had been unearthed in the area, Defence Ministry officials said.

Hundreds of tonnes of unexploded bombs from the war remain buried in Japan. They are sometimes dug up at construction sites.