Addis Ababa - Swarms of locusts have invaded north-west Ethiopia, posing a serious threat to crops there and putting the region, as well as the entire Horn of Africa, at risk of further food insecurity, officials said on Monday.

Just over a week since the United Nations Food and Agriculture Organisation (FAO) warned of new locust hordes descending on Eritrea and Sudan after devastating swarms hit west and northern Africa last year, Ethiopian authorities said the pests had already been spotted in Tigray and Amhara districts.

"Some groups of locusts, most probably coming from Sudan have flown into different localities in Tigray and Amhara," said Fikre Markos, the head of the crop protection department at Ethiopia's agriculture ministry.

Peter Odiyo, director of the desert locust control organisation for eastern Africa, said aerial surveillance had been mounted to try to track the swarms but that one main group appeared to have split up making such efforts difficult.

"It is now flying in different groups, that is why it is difficult to get an idea of the size of the whole population", he said.

"This is worrying considering that these locusts have been troubling the whole of western Africa for several months and they are now extending towards the east," Odiyo said.

Most troubling, he said, was the potential for the locusts to lay eggs thereby increasing their possible devastation by reproducing and placing both human and livestock food stocks at risk.

"The food security part is the main concern because by damaging crops they also damage livestock and wildlife, so that the cattle might also die, not having enough grass to eat," Odiyo said.

About 85 percent of Ethiopia's 72-million inhabitants depend on subsistence agriculture and were badly affected by the last serious locust invasion in 1995, officials said.

Last year, huge swarms invaded the countries of the Sahel in north-west Africa causing extensive damage in the worst locust upsurge in 15 years.

The FAO, regional countries and the international community spent more than $200-million in combating it.