"We are witnessing the starving and the crippling of an entire generation," said Guterres, who called the situation in Yemen the world's greatest humanitarian crisis. "We must act now to save lives."
A half-million children are so severely malnourished that they are likely to die if they do not receive urgent care, said the UN children's agency and the World Food Programme.
The fundraising conference in Geneva fell short of hopes, much like the UN's fundraising call in March for famine prevention in Yemen, South Sudan, Somalia and Nigeria.
In an irony, Saudi Arabia has made the biggest funding pledge, promising US$150 million for Yemen.
Much of the physical destruction in the country has been wrought by a Saudi-led air campaign - backed by the United States and others - that human rights activists say has indiscriminately targeted civilians.
The United Arab Emirates, a key member of the coalition, pledged US$100m. The US said it was committing nearly US$94m in additional assistance, bringing its total to US$526m since the 2016 fiscal year.
The war in Yemen has pitted the Saudi-backed mostly Sunni Government against Shia rebels known as Houthis. The Houthis control the capital, Sanaa, as well as much of Yemen's western coast, including the pivotal port of Hodeida.
Yemen imports 90 per cent of its food, and 70 per cent of that comes through Hodeida, which the Saudi navy is blockading, letting only a trickle through.
Reports have swirled recently about an impending assault on the city, Yemen's fourth-largest, by Saudi forces. About 100,000 internally displaced people live there.
The Saudis claim that the port serves as an entry point for weapons supplies to Houthis, but aid agencies have voiced scepticism at the claim, given the blockade and the fact that the UN inspects each arriving ship.
The trigger for famine could be an assault on Hodeida. If even the severely restricted flow of food is disrupted and fighting limits access to aid agencies, those living day to day will be without any other option.
"We are concerned about facilities in Yemen because at this stage we can't afford to even lose one bridge or one road network, let alone lose a major facility like the Hodeida port," Muhannad Hadi, regional director for the World Food Programme, said.
Guterres acknowledged aid is only a stopgap measure, insisting that Yemen's suffering will only ease with a political solution that ends the war.