While about 16 million people need urgent help, 20.7 million Yemenis need some humanitarian assistance, including 12.1 million people in acute need, Xinhua news agency quoted Stephane Dujarric, the chief spokesman for UN Secretary-General Antonio Guterres, as saying at a briefing on Wednesday. 

Yemen's currently faces the largest humanitarian crisis in the world. 

The UN estimates Yemen's population at more than 30 million people. 

"Yemen continues to be the world's worst humanitarian crisis and the largest aid operation," Dujarric said. 

"Famine is stalking the nation, with more than half the population facing acute food insecurity and record levels of acute malnutrition among children under 5." 

The spokesman noted that last year's plan was only 56 per cent funded and some critical programs had to be closed as a result. 

"We are doing everything we can to help, but we need adequate funding as needs continue to rise," he told the briefing. 

"At the high-level pledging event that took place in early March, donors pledged only $1.7 billion for the response, that's less than half what is required (for 2021). 

"The Secretary-General said the pledges represent at best a down payment. We urge donors to quickly disburse their pledges and scale up funding for the humanitarian response to save lives. 

"And if people have not yet pledged, it is never too late to do so," Dujarric added. 

Yemen has been mired in civil war since late 2014 when the Iran-backed Houthi rebels seized control of several northern provinces and forced the Saudi-backed government of President Abd-Rabbu Mansour Hadi out of the capital Sanaa.