A United Nations agency has warned a pest, which could threaten food security, is likely to spread from India to other parts of Asia.

South East Asia and South China are most at risk from the fall armyworm, the Food and Agriculture Organisation (FAO) says.

Recently detected in India - the first time it has been found in Asia - the crop-eating insect has the capacity to fly over long distances (100km per night) and ravage crops all year round, given the region's tropical climate.

The FAO says this means there are always crops and weeds around that the fall armyworm can feed on.

They can eat maize and some 80 other crops - including rice, vegetables, groundnuts and cotton.

FAO assistant director-general Kundhavi Kadiresan said: "Fall Armyworm could have a devastating impact on Asia's maize and rice producers - mostly small-scale farmers who depend on their crops for food and to make a living.

"This is a threat that we cannot ignore".

In Asia - where small-scale farmers cultivate about 80% of the region's farmlands - rice and maize are among the most produced and consumed cereals.

The fall armyworm | Image: Food and Agriculture Organization (FAO)

Over 200 million hectares of maize and rice are cultivated annually in Asia.

China is the second-largest maize-producing country in the world, and over 90% of the world's rice is produced and consumed in the Asia-Pacific region.

Native to the Americas, the fall armyworm has already spread across Africa - where it was first detected in early 2016.

By early 2018, all but 10 African states and territories reported infestations.

The FAO is asking farmers and member states in Asia to implement the Fall Armyworm Monitoring and Early Warning System (FAMEWS) to monitor, analyse and produce early warnings - including risk to food security.

It also wants them to produce "accurate estimates" of potential crop-loss, based on the FAMEWS data.