World Health Organisation Director-General Tedros Adhanom Ghebreyesus says a recent spike in COVID-19 cases in some countries in Europe and North America presents leaders with a "critical moment for action".
"This is another critical moment for action," he said.
"Another critical moment for leaders to step up. And another critical moment for people to come together for a common purpose. Seize the opportunity, it's not too late."
Tedros was addressing a regular WHO news briefing in Geneva from self-isolation at home after announcing on Twitter that he had been in contact with a person infected with COVID-19.
France, Germany, Italy, the United Kingdom, the Netherlands and other countries have announced second lockdowns or strict new curbs as infections surge.
"I am not optimistic that in just four weeks we will lower the number of new cases to the level announced by the president (5000 new cases per day)," said epidemiologist Dominique Castigliola, director of research at France's National Institute of Health and Medical Research.
"We will need more time. I don't think we'll be able to hold big family meals at Christmas. That seems very unlikely to me."
German Chancellor Angela Merkel said on Monday people must show discipline if the country's new shutdown is to be lifted in time for Christmas, adding that the country's health system was at stake.
"Throughout the winter months, we will have to limit private contacts," she told a news conference.
"The light at the end of the tunnel is still quite a long way off."
British Prime Minister Boris Johnson on Monday defended a second lockdown in England from critics who said it was unnecessary and others who said it was too late, arguing now was the time to prevent a "medical and moral disaster".
After rejecting calls last month for a new lockdown, Johnson announced new restrictions across England would begin at Thursday morning and last until December 2.
More than 46.37 million people have been infected globally and 1,198,168 have died from the respiratory disease, according to a Reuters tally.
The United States leads the world with more than 9 million cases and 230,700 deaths.
Iran, the Middle East country worst hit by COVID-19, reported a record 440 deaths in the past 24 hours.
But Belgium, which is proportionally the worst-hit country in Europe when it comes to coronavirus cases, announced on Monday that it is finally starting to see "some points of light" amid the dire statistics of the past weeks.
Some critical statistical curves are starting to ease their upward rise, increasing hopes that measures taken in parts of the country last month are beginning to pay off.
"The number of infections and hospital admissions continue to rise but not as fast anymore," said virologist Steven Van Gucht of the Sciensano government health group.
"The high-speed train is somewhat easing up, even if it still rages on."
Despite such numbers, Van Gucht said that cases now rose at an adjusted 29 per cent, "which is considerably lower than the past weeks, when increases were 100 per cent on a weekly basis".
There were fears that the capacity of beds in the intensive care units would have been reached by Friday but Van Gucht said that the increase was somewhat slower there too.
Meanwhile, India has added 45,230 new coronavirus infections in a continuation of a downturn in cases.
The health ministry also reported 496 more fatalities on Monday, raising the death toll to 122,607.
With 8.2 million cases, India is the second worst-hit country behind the US but the number of new cases being diagnosed each day is falling steadily even though testing is not declining.
In the last week, there have been fewer than 50,000 new cases every day.