With 20 million Yemenis in need of immediate assistance in the face of conflict and the Covid-19 pandemic, "the humanitarian situation is falling off a cliff" in the war-torn country, the UN said.
Of those, more than 16 million people are going hungry this year, tens of thousands of people are already living in famine-like conditions, and 5 million more are just one step away, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said on Thursday.
Add to that are surging Covid-19 infections, with hospitals and health facilities reportedly turning away patients due to lacking treatment resources, reports Xinhua news agency.
Conflict has been escalating, particularly in Marib, where an offensive by Houthi forces has so far displaced nearly 20,000 people and threatens the safety of millions.
Further complicating the situation, the rain season is underway, with more than 22,000 people affected by floods.
Most of those victims are displaced people living in inadequate shelters.
Aid agencies are seeking $3.85 billion to block a massive famine, respond to the Covid-19 surge and meet other critical needs this year, OCHA said.
However, the response plan is only 34 per cent funded.
The aid operation in Yemen previously was able to help nearly 14 million people a month.
Now it's down to about 10 million people a month, mainly because of funding cuts, OCHA added.
Last year, aid agencies received only half of the funds needed, forcing them to cut back aid and shut down programs.