The United Nations said it needed $4.3 billion this year to help millions of people in war-ravaged Yemen, ahead of a donors' conference on Monday.
Aid agencies need the money to help more than 17 million people in the country, which has been devastated by an eight-year civil war.
The conflict has claimed hundreds of thousands of lives and plunged the poorest country on the Arabian Peninsula into one of the world's worst humanitarian tragedies.
Yemen is also at the forefront of the climate crisis, with severe drought and flooding threatening lives, the UN said.
It acknowledged that "record global humanitarian needs are stretching donor support like never before".
"But without sustained support for the aid operation in Yemen, the lives of millions of Yemenis will hang in the balance, and efforts to end the conflict once and for all will become even more challenging," it said in a statement.
In 2015, a Saudi-led coalition intervened to back the government after the Huthis seized control of the capital Sanaa and large swathes of the country.
A truce that began on April 2 last year expired on October 2.
UN chief Antonio Guterres, who will attend Monday's donor conference in Geneva, said the international community had "the power and the means to end this crisis".
"And it begins by funding our appeal fully and committing to disbursing funds quickly," he said in the statement.
Last year, the UN raised more than $2.2 billion to enable aid agencies to reach nearly 11 million people across the country every month.
