UN aid agencies are warning that three quarters of the programmes they back in Yemen will have to close in the next few weeks without more funding, even as the coronavirus and other diseases spread.
There are fears that the Covid-19 outbreak there could be worse than thought.
A five-year conflict between a Saudi-led coalition in the south and the Iran-aligned Houthi group in the north has left most Yemenis reliant on aid.
The malnourished population has among the world's lowest immunity levels to coronavirus.
"Our office has received reports of hospitals turning away sick people, some of whom were struggling for breath and with a high fever", Rupert Colville, Spokesperson for the Office of the UN High Commissioner for Human Rights (OHCHR) said.
"There are simply no beds, little equipment, few staff and next to no medicine available. Sanitation and clean water are also in short supply. The country has officially recorded more than 500 cases of Covid-19. However, official reports are lagging far behind actual infections, especially in areas controlled by the de facto authorities in the north. The overall case fatality rate is over 20 percent", he said.
Many functioning health centres in Yemen lack basic equipment to treat Covid-19.
"Health workers have no protective gear, and most are receiving no salaries, resulting in health workers not reporting to duty", Mr Colville added.
Yemen has reported 564 cases of Covid-19, but the figures may not include all cases in areas controlled by the Houthi authorities in the north.
It has reported 130 related deaths, though aid agencies have said testing levels are low so the real numbers are impossible to determine.
International donors promised $1.35 billion for Yemen at a conference earlier this month, short of a UN target of $2.4 billion.
Only half has been paid so far.
"Despite Covid being a global pandemic and each country may be focusing on containing the spread of the virus, one can only imagine the havoc the virus can cause to a country like Yemen, where children and their families are bearing the brunt and consequences of over five years of conflict, cholera, diseases; and a fragile health system", Bismarck Swangin, UNICEF Yemen said.
"It's important that donors who have supported Yemen, continue to step up, so that the investments and gains made are not reversed", he said.
The UN children's agency UNICEF said water, sanitation and hygiene services for 4 million people would start shutting down in July if it did not get $30 million by the end of this month.
"Of 8.4 million Yemenis whose access to WASH (water, sanitation and hygiene) will be affected because of insufficient funding, a total of 4 million people, nearly half of them children, directly depend on UNICEF.
They are among the most vulnerable Yemenis due to conflict, cholera and internal displacements.
With Yemen’s healthcare system on the brink of collapse due to malaria, cholera and other diseases and now Covid -19, the situation there is now described as "desperate".