"They missed building up the necessary infrastructure during the summer months, after they brought the first wave under the control," the WHO's David Nabarro said in an interview with Swiss newspapers.

"Now we have the second wave. If they don't build the necessary infrastructure, we'll have a third wave early next year," said Nabarro, a Briton who campaigned unsuccessfully to become the WHO director general in 2017.

Europe briefly enjoyed sinking infection rates that are now surging again: Germany and France on Saturday saw cases rise by 33,000 combined, Switzerland and Austria have thousands of cases daily, while Turkey reported a record 5,532 new infections.

Nabarro singled out Switzerland's move to allow skiing - with masks required in gondolas - as other Alpine nations like Austria have shuttered resorts. Nabarro said Switzerland could reach a "very high level of sicknesses and deaths".

"Once the infection rates sink, and they will sink, then we can be as free as we want," Nabarro was quoted as saying by the Solothurner Zeitung. "But right now? Should ski resorts open? Under what conditions?"

Nabarro lauded the response of Asian countries like South Korea, where infections are now relatively low: "People are fully engaged, they take on behaviours that make it difficult for the virus. They keep their distance, wear masks, isolate when they're sick, wash hands and surfaces. They protect the most endangered groups."

Nabarro also said Asia did not relax restrictions prematurely.

"You must wait until case numbers are low and stay low," he said. "Europe's reaction was incomplete."

Australian Associated Press