The World Food Programme (WFP) has denounced the blocking of humanitarian convoys by armed groups in Ethiopia's Tigray region, where four million people face a food crisis, including 350,000 risking famine.

The United Nations agency said in a statement it had deployed more than 180 staff in an emergency food operation to reach 1.4 million people, "yet that is barely half of the number we should be reaching".

"The brutal reality for our staff in Tigray is that for every family we reach with life-saving food, there are countless more especially in rural areas whom we cannot reach," said WFP Executive Director David Beasley.

"We have appealed for humanitarian access but are still being blocked by armed groups."

Ethiopian Prime Minister Abiy Ahmed, winner of the 2019 Nobel Peace Prize, sent troops into the northern region in November to detain and disarm leaders of the Tigray People's Liberation Front, the region's former ruling party.

He said the move came in response to TPLF attacks on federal army camps.

Though he vowed the conflict would be brief, more than six months later fighting continues, reports of atrocities including the widespread use of rape are proliferating, and many leaders are warning of a major catastrophe.

Today, new data from the Integrated Food Security Phase Classification (IPC), a widely used standard for classifying food security, showed that 350,000 people in Tigray fell into the lowest level of the scale, the Phase 5 "catastrophe/famine" category.

That was the largest number of people who had fallen into that level since the 2011 famine in Somalia.

Half of mothers and nearly a quarter of children visited by the WFP in 53 Tigrayan villages were malnourished, Beasley said.

The WFP called for an end to hostilities, unimpeded access to those living in Tigray, and new donor funding.

The UN's top emergency relief coordinator has estimated that 90% of the region's harvest has been lost due to looting or destruction, while 80% of the livestock has been looted or slaughtered.