ROME -- Air raid sirens sounded across China and flags flew at half staff in tribute Saturday to victims of the coronavirus pandemic, including the health care "martyrs" who have died fighting to save others.

With the highest number of infections in Europe and their hospitals overwhelmed, Spain and Italy struggled to protect medical staff on the front lines of the outbreak, while 17 medics in Egypt's main cancer hospital tested positive for the virus.

As the number of infections has grown to more than 1.1 million worldwide, health care systems are straining under the surge of patients and lack of medical equipment like ventilators as well as protective masks and gloves, giving rise to growing concerns about the exposure of hospital personnel.

Italy and Spain, with combined deaths of more than 25,000 and nearly a quarter-million infections, have reported a high percentage of infections among health care workers.

Carlo Palermo, head of Italy's hospital doctors' union, fought tears as he told reporters in Rome of the physical risks and psychological trauma the outbreak is causing, noting reports that two nurses had committed suicide.

"It's a indescribable condition of stress. Unbearable," he said. "I can understand those who look death in the eye every day, who are on the front lines, who work with someone who maybe is infected, then a few days later you see him in the ICU or die."

U.S. President Donald Trump announced late Friday he would prevent the export of N95 protective masks and surgical gloves to ensure they are available in the U.S. -- prompting neighbouring Canada's prime minister to respond that cross-border aid goes well beyond supplies.

"I think of the thousands of nurses who cross the bridge in Windsor to work in the Detroit medical system every day," Justin Trudeau said. "These are things Americans rely on."

The number of people infected in the U.S. has now exceeded a quarter-million, with the death toll climbing past 7,000. New York state alone accounts for more than 2,900 dead, an increase of over 560 in just one day. Most of the dead are in New York City, where hospitals are swamped with patients.

World Health Organization director-general Tedros Adhanom Ghebreyesus warned African leaders of an "imminent surge" in coronavirus cases on the continent, urging them to open humanitarian corridors to allow the delivery of badly needed medical supplies.

More than half of Africa's 54 countries have closed air, land and sea borders to prevent the virus' spread but that has delayed aid shipments. Virus cases in Africa are now over 7,700, and the head of the Africa Centers for Disease Control and Prevention has warned some nations will have more than 10,000 cases by the end of April.

In the Philippines, Sen. Richard Gordon, who is also head of the local Red Cross, said lockdown measures have meant millions of poor families are unable to fulfil basic needs.

"A lot of people are hungry. They're asking for milk, they're asking for diapers. They say it's not going fast enough," Gordon said, threatening to have local officials arrested if they steal from government aid for dirt-poor families.

Eleven Russian military planes carrying disinfection experts landed in Serbia on Saturday, which Serbian Defence Minister Aleksandar Vulin said shows "that we are not alone."

The transport followed last month's deployment of a similar Russian coronavirus task force to Italy and the delivery of medical supplies to the United States. Russian officials have angrily rejected claims that the Kremlin is seeking political gain by providing aid to other countries.

Russia has reported a relatively few 4,700 cases and 43 deaths, and its southern neighbour Georgia said Saturday it has registered its first death from the virus, among 156 confirmed cases of infection.

In China, where the coronavirus was first detected in December, authorities have cautiously lifted restrictions amid dropping numbers of infections. On Saturday it reported just one new confirmed case in the epicenter of Wuhan and 18 others among people arriving from abroad. There were four new deaths for an official total of 3,326.

In the nationwide tribute to the victims, the government singled out the more than 3,000 health care workers who contracted COVID-19 and the 14 reported to have died from the disease. Among them was doctor Li Wenliang, who was threatened with punishment by police after publicizing news of the outbreak but has since been listed among the national "martyrs."

As the outbreak spreads in Egypt, the Arab world's most populous country, the news that 17 health care worker tested positive for the virus at the National Cancer Institute raised fears of what the virus might do to the country's hospital system.

Maggie Mousa, an anesthesiologist at the institute, tweeted that one of her close friends was infected. She accused top officials of negligence for not imposing restrictions after the first case was detected more than a week ago.

"They refused to take any measures to protect her and isolate the institute," she said.

Spain's Health Ministry reported 18,324 infected health workers as of Saturday, representing 15% of the total number of infections in the country. To help boost its ranks of health workers, Spain's government said that it had hired 356 foreign health workers living in Spain. It has also hired medical and nursing students to help.

After seeing commercial shipping lines break down, the government has started flying in medical supplies from China on military cargo planes. Meanwhile, local industry is shifting to producing masks, protective suits, and breathing machines.

As the country completes its third week in a state of emergency, there were signs the number of new infections were slowing, but they were still high with 7,026 new cases reported overnight Saturday and 809 deaths.

In Italy, more than 11,000 medical personnel have been infected -- just under 10% of the official total -- and some 73 doctors have died, according to the National Institutes of Health and the association of doctors.

Significantly, not all the doctors were working in hospitals. Many were general practitioners or dentists, who were believed to have been exposed via respiratory droplets.

Palermo, the doctors' union head, said a key reason for the high contagion rate among general practitioners was that flu was raging at the same time in the early part of the year.

"The epidemic was superimposed on top of the normal course of influenza, which didn't allow us to discriminate between the two," he said.

"A patient with a fever or cough or unspecific symptoms would go to his doctor, who would see him at home or in his office, and that's where the contagion happened."

Worldwide, confirmed infections rose past 1.1 million and deaths exceeded 60,000, according to a tally by Johns Hopkins University. Experts say both greatly under-count the true number of victims because of lack of testing, mild cases that were missed and governments that are underplaying the crisis.

At the same time, more than 233,000 people have recovered from the virus, which causes mild to moderate symptoms in most patients, who recover within a few weeks.

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Rising reported from Berlin, Wilson reported from Barcelona. Associated Press writers around the world contributed to this report.