A $392 million appeal was made by the World Health Organisation on Sunday for Yemen to avert a “potential collapse” of its health sector.
The country faces one of the world's worst humanitarian crises following years of war between the Iran-backed Houthi rebels and the internationally recognised government.
About half of all health facilities in Yemen are partly functioning or are completely out of service because of shortages of staff, funds, electricity, medicines, supplies and equipment, the WHO said.
“Yemen requires urgent and robust support … to effectively avert the potential collapse of its health system,” said the agency's Yemen representative Adham Abdel Moneim Ismail.
“New funding in the amount of $392 million is required” to ensure that health facilities can continue providing services to 12.9 million people, he added.
Those needing assistance include 540,000 children under five who face severe acute malnutrition with a direct risk of death, said Mr Ismail.
His appeal came a day before the donor meeting being organised by the UN, Switzerland and Sweden.
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.
The UN said it needed $4.3 billion to raise this year to help millions Yemenis.
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 UN estimates that 21.6 million people — two-thirds of Yemen's population — will require humanitarian aid and protection services in 2023.
On top of a humanitarian crisis, Yemen also faces a 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.
Houthi rebels seized the capital Sanaa in 2014, ousting the government and pushing it to call for assistance by a Saudi-led coalition.
It comes as a container ship carrying general commercial goods docked at the country's main port of Hodeidah for the first time since at least 2016 on Saturday as warring parties are in talks to reinstate an expired UN-brokered truce deal.
Goods arriving at Hodeidah have to be vetted by the UN Verification and Inspection Mechanism for Yemen established to prevent arms shipments from entering the country.
In the past seven years, the Djibouti-based UNVIM has given approval only to ships carrying specific goods such as food, fuel and cooking oil.
Granting access to commercial ships was a trust-building step aimed at supporting Saudi-Houthi talks to reinstate the truce, which expired in October, an official in the Yemeni government told Reuters.