Vital oxygen supplies to treat patients sick with Covid and other critical illnesses, including war injuries, are running dangerously low in Ukraine.
The World Health Organization says lorries have been unable to carry supplies from plants to hospitals in the country, including capital Kyiv.
And stocks could run out within the next 24 hours.
The WHO is working with partners to transport urgent shipments through Poland.
“The oxygen supply situation is nearing a very dangerous point,” WHO director general Tedros Adhanom Ghebreyesus and regional director for Europe Hans Kluge said.
“Some [hospitals] have already run out.
“This puts thousands of lives at risk.”
An estimated 1,700 patients admitted to hospital in Ukraine because of Covid will probably need oxygen treatment.
But it is also needed for a range of other conditions, including childbirth.
The WHO says several manufacturing plants in Ukraine are also facing shortages of zeolite – a crucial, mainly imported chemical product needed to make safe medical oxygen.
Hospital services are also under threat from electricity and power shortages.