In Belgium, all nonessential hospital work has been postponed to deal with an influx of new Covid-19 patients, whose numbers have nearly doubled in the past week, matching levels seen in the first wave of the pandemic in the spring.

Croatia has asked former doctors to come out of retirement to help in hospitals, while National Guard troops have flown from the United States to the Czech Republic to assist overwhelmed health care professionals there.

In the Netherlands, new coronavirus patients have had to be transferred by helicopter to Germany to relieve Dutch intensive-care units.

Across Europe, hospitals are filling up at an alarming pace that harks back to the darkest hours of the first wave of the pandemic in the spring. The authorities are scrambling to slow the spread of a virus that threatens to bring ailing health care systems to the brink of collapse.

Worldwide, more than 500,000 cases were tallied on Wednesday, a record since the start of the pandemic. All 20 countries with the highest rates of new cases over the last week are in Europe. Britain, France, Italy and Spain were among the countries that recorded their highest death tolls in months.

In announcing a new nationwide lockdown in France on Wednesday, President Emmanuel Macron predicted that the second wave of the virus would be more deadly than the first.

In France, one million people are currently estimated to be infected with the coronavirus, and 2,000 new patients are hospitalized every day, according to government data, the highest numbers in the country since mid-April. Doctors have warned that hospitals won’t hold in the winter if the virus can’t be stemmed, and Mr. Macron bluntly said on Wednesday that if France couldn’t put the brakes on the pandemic, doctors would soon have to choose which Covid-19 patients to save.

In Germany, as hospitalizations have doubled in the past 10 days and nearly 1,500 patients are in intensive care, Chancellor Angela Merkel announced new lockdown measures on Wednesday as she vowed to avoid “situations that are extremely difficult.”

Exhausted health care workers and other epidemics, like the flu, that arrive in winter have led authorities to warn that the worst is yet to come. While in Western Europe, the fear of overwhelmed hospitals brought a feeling of déjà-vu from the first wave in the spring, countries in Central and Eastern Europe, which escaped the first wave relatively unscathed, have faced a frighteningly new situation.

Countries like the Czech Republic and Poland imposed tough restrictions in the spring and saw lower infections rates, but soaring cases this fall have laid bare a critical shortage of nurses, doctors, and intensive care beds. In Bulgaria, scores of health care professionals are falling ill with the virus, and an acclaimed doctor became the 19th medical professional there to die of the virus earlier this month. In the Czech Republic, where cases are rising at one of the fastest paces in Europe, Prime Minister Andrej Babis has warned that the country’s health care system could collapse before mid-November.

“What happened was somehow predicted but nobody expected its scope,” Mr. Babis said after declaring a second national lockdown.