A Yemen aid summit in Geneva on Tuesday received $150 million from Saudi Arabia and $100 million from Kuwait.
The UN is seeking $2.1 billion for Yemen this year as it has received only 15 percent toward that appeal.
Yemen is reeling from conflict between Houthi militias, aligned with Iran, against a Western-backed, Arab coalition.
At least 10,000 people have been killed in the fighting.
Some 17 million of Yemen's 26 million people lack sufficient food and at least three million malnourished children are in "grave peril", Stephen O'Brien, UN Emergency Relief Coordinator said.
"This is rapidly becoming the world's worst humanitarian disaster," he told Reuters.
"I would urge the region in particular to step up to support the Yemeni people caught up in this conflict."
UN aid agencies are reaching more than 5 million Yemenis "despite all the bureaucratic obstacles and the difficulties of access including at the ports", O'Brien said.
The United Nations has already declared famine in parts of South Sudan and warned of looming famine in Somalia, South Sudan and Yemen.
Oxfam called on donor nations to step up life-saving assistance rather than providing arms to fuel the deepening conflict.