The US is thought to have dropped the 89cm-long (3ft) device during WW2.

It was found by workers building a car Park on the site where the decommissioning process has been going on for four decades.

Tens of thousands of residents were forced to flee the area after a reactor accident in 2011 following an earthquake and tsunami.

The incident at the facility Tokyo Electric Power Co (Tepco) has become the most serious nuclear accident in the world since Chernobyl in 1986.

No one died directly in the crisis, but three former Tepco executives will stand trial on negligence charges over deaths linked to the evacuation of the area.

According to TEPCO, construction work was immediately suspended after the facility was discovered, and temporary no-go zones were deployed while bomb disposal experts were deployed.

It is not uncommon for unexploded WW2 devices to be found in Japan more than 70 years after the end of the war.

The Fukushima area was previously home to a Japanese military base.