A 250-kilo US air bomb was discovered by a local near Vurberk Castle by means of a metal detector last week while he was playing a treasure hunt game with his kids.

Instead of alerting authorities of the find right away, the man unearthed the bomb and transported it by his lorry to his home yard near the village church. Only then did he call the police.

"Given the type of the bomb, the gentleman was very lucky. This could've ended badly," Igor Boh from the state unexploded ordnance defence unit told reporters in Duplek.

"Since the bomb has been removed from the location where it was dropped during bombing and handled as it shouldn't have been, changes may have developed that could cause an uncontrolled explosion," he said.

A further aggravating factor is that this is the first such bomb discovered in Slovenia. It has a chemical ignition mechanism and in similar cases abroad dismantling teams have been hurt.

The bomb founder's family has already been evacuated and the area within a 300-metre radius of the bomb has been sealed off. Access to the castle and church is being blocked by police and firefighters.

The operation to deactivate the bomb will be very demanding and is expected to be carried out on Tuesday, when an area within a one-kilometre radius will have to be evacuated, which means 400 people.

Until then, the authorities say there is no reason for concern because the bomb is safe as long as left as it is. If all goes according to plans, the device should be dismantled within a few hours.

The man who found the bomb could face public nuisance charges, a crime that carries up to five years in prison. A police investigation is under way.