"Many countries in the northern hemisphere are seeing a concerning rise in cases and hospitalisations," WHO Director General Tedros Adhanom Ghebreyesus told reporters in Geneva on Monday.

"Intensive care units are filling up to capacity in some places, particularly in Europe and North America."

More than 40 million people around the world have tested positive for the novel coronavirus since the pandemic began and more than one million have died of COVID-19, the disease it causes.

Tedros said he understood the "pandemic fatigue" that people were feeling as a result of lockdowns.

"Working from home, children being schooled remotely, not being able to celebrate milestones with friends and family or not being there to mourn loved ones - it's tough and the fatigue is real," he said.

But, he said, "We cannot give up. Leaders must balance the disruption to lives and livelihoods with the need to protect health workers and health systems as intensive care fills up."

He also urged leaders to follow the advice of experts and stop using the virus as a political football.

"Where there has been political division at the national level; where there has been blatant disrespect for science and health professionals, confusion has spread and cases and deaths have mounted," he said.

"This is why I have said repeatedly: stop the politicisation of COVID-19."

Australian Associated Press