Millions of men, women and children in war-torn Yemen are facing famine - again, top United Nations officials warned on Wednesday as they appealed for more money to prevent it - again.

"We are on a countdown right now to a catastrophe," U.N. food chief David Beasley told the U.N. Security Council. "We have been here before ... We did almost the same dog-and-pony show. We sounded the alarm then."

The United Nations describes Yemen as the world's largest humanitarian crisis, with 80% of the people in need of help.

"If we choose to look away, there's no doubt in my mind Yemen will be plunged into a devastating famine within a few short months," Beasley told the 15-member council.

A Saudi Arabia-led military coalition intervened in Yemen in 2015, backing government forces fighting the Iran-allied Houthi group. U.N. officials are trying to revive peace talks to end the war as the country's suffering is also worsened by an economic and currency collapse and the COVID-19 pandemic.

In late 2017, U.N. aid chief Mark Lowcock warned that Yemen was then facing "the largest famine the world has seen for many decades with millions of victims".

"We prevented famine two years ago," Lowcock told the Security Council on Wednesday. "More money for the aid operation is the quickest and most efficient way to support famine prevention efforts right now."

He said the world body had received less than half of what it needed - about $1.5 billion - this year for its humanitarian operations in Yemen. Last year it received $3 billion.

"When I think about what famine would mean, I am really at a loss to understand why more is not being done to prevent it," Lowcock said. "It is a terrible, agonizing and humiliating death ... Yemenis are not 'going hungry'. They are being starved."