The United Nations warned on Monday of the potential "massive destruction" of the world's banana crop if a disease affecting the most popular variety spreads from Asia to Africa and the Middle East.

The disease is "posing a serious threat to production and export" of bananas, the fourth most important food crop for the world's least developed countries, the Rome-based Food and Agriculture Organisation (FAO) said in a statement.

"Countries need to act now if we are to avoid the worst-case scenario, which is massive destruction of much of the world's banana crop," Fazil Dusunceli, a plant pathologist at FAO, was quoted as saying.

Gianluca Gondolini, secretary of the World Banana Forum, said it could hurt "employment and government revenues in many tropical countries".

The TR4 strain of Panama disease, which is one of the world's most destructive and affects the Cavendish variety -- the most popular in global exports.

FAO said it had already caused significant losses over the last two decades in Southeast Asia and cases had recently been reported in Jordan and Mozambique.

It has not yet affected top global exporters such as Colombia or Ecuador.

The disease is soil-borne and the fungus can remain viable for decades and is not dangerous to humans.

The FAO said there was a need for more monitoring, prevention and training for farm workers, including measures to avoid movement of infected soil and planting materials into and out of farms.