Doctors Without Borders (MSF) warned Wednesday it will run out of masks within three to four weeks, putting millions at risk if the medical charity has to halt its operations.
MSF, which is on the front line fighting the coronavirus pandemic in some of the world's poorest countries, appealed for any help it could get in keeping its medics supplied with protective equipment.
And it warned of knock-on consequences for the health emergencies it was already tackling before the COVID-19 outbreak struck.
"We have stocks, globally, for three, maybe four weeks maximum," said Kenneth Lavelle, MSF's deputy director of operations, from a virtual press conference in Geneva, where the organisation is based.
"The small quantities that remain will be distributed to our missions, but we have got virtually zero visibility on what stocks we will have in three to four weeks.
"Our supply pipeline will be empty."
He said Medecins Sans Frontieres would need roughly around a million masks a week for the next six months.
Otherwise, "we might be faced with taking even more difficult decisions about stopping activities", said Lavelle.
MSF, which has around 50,000 staff operating in 65 countries, said it was concerned about the knock-on effects of having to scale back other activities, such as routine immunisations, to concentrate on fighting COVID-19 -- not to mention the results of having to down tools altogether.
"The consequences go way, way beyond what we're trying to respond to today," said Lavelle.
In its response to the coronavirus pandemic, MSF is focusing its efforts on supporting local authorities in caring for patients, protecting the vulnerable and keeping essential medical services running.
Trish Newport, MSF's emergency coordinator for the Democratic Republic of the Congo, warned of the dangers of scaling back operations in countries with fragile health systems.
"If we're not able to continue providing care safely, we will see an increase in mortality of non-COVID-19-related things: malaria, diarrhoea, maternal health," she said.
"We also would have limited capacity to be able to respond to an emergency outbreak, such as the measles outbreak in the Congo or in Chad, or other possible outbreaks such as cholera."
Due to the phenomenal demand for masks, MSF said it is finding itself priced out of the market.
The humanitarian non-governmental organisation urged governments and commercial companies to help them get personal protective equipment.
"We would be delighted to engage with them to see if they could help us to address these shortages," said Lavelle.
Asked if millions of people would potentially be at risk if the shortage persists, he said: "That would not be exaggerating".