The World Health Organization, or WHO, on Monday warned that medical masks should be prioritized for health workers as countries consider measures to protect their mass population from COVID-19.

The United States' Centers for Disease Control and Prevention, or CDC, revised its guidance last week, saying that it recommends wearing cloth face covering in public settings where other social distancing measures are difficult to maintain, especially in areas of significant community-based COVID-19 transmission.

The US is the latest epicenter of the novel coronavirus outbreak. By 7pm CEST Monday there were 338,995 confirmed cases in the US, according to the John Hopkins University Coronavirus Resource Center.

Austria, the Czech Republic and several other countries have made wearing a mask compulsory in supermarkets and some other public places.

WHO Director-General Tedros Adhanom Ghebreyesus said he understands that some countries have recommended or are considering the use of both medical and non-medical masks in the general population to prevent the spread of COVID-19.

"First and foremost, medical masks should be prioritized for health workers on the front lines of the response," he told a virtual media conference from Geneva. "We know medical masks can help to protect health workers, but they're in short supply globally."

Tedros expressed concern that the mass use of medical masks by the general population could exacerbate the shortage of specialized masks for those who need them most.

"In some places, these shortages are putting health workers in real danger," he said.

The WHO continues to recommend the use of medical masks, respirators and other personal protective equipment for health workers in medical facilities as well as the use of medical masks by people who are sick, and those who are caring for a sick person at home.

Tedros said that the WHO has been evaluating the wider use of medical and non-medical masks for COVID-19, adding that there is limited research in this area. On Monday, the WHO issued guidance and criteria to support countries in making that decision.

Tedros cautioned that masks should only ever be used as part of a comprehensive package of interventions. "Masks alone cannot stop the pandemic," he said. "Countries must continue to find, test, isolate and treat every case and trace every contact."

On Monday, the European Union announced that a Chinese plane had arrived in Rome with a donation of 2 million surgical masks, 200,000 N95 masks and 50,000 testing kits for Italy.

"We are grateful for China's support and, as President von der Leyen stated, we need each other's support in times of need," said Janez Lenarcic, European Commissioner for Crisis Management. "The EU and China have been working together since the beginning of the coronavirus outbreak."

In February, the EU donated 56 tons of medical supplies to China when the country was at the height of the COVID-19 outbreak.

China is one of the world's leading medical protective equipment manufacturers. According to Chinese customs official on Sunday, the country has exported 3.86 billion masks, 37.5 million pieces of protective clothing, 16,000 ventilators and 2.84 million COVID-19 testing kits to more than 50 countries since March 1.

Tedros revealed on Monday that more than 70 countries have joined WHO's solidarity trial, to accelerate the search for an effective treatment, and that around 20 institutions and companies are racing to develop a vaccine.

"WHO is committed to ensuring that as medicines and vaccines are developed, they are shared equitably with all countries and people," he added.