Failures in COVID-19 response strategies this year have created the ideal conditions for a deadly new variant to emerge, as infections have increased in parts of China, according to the World Health Organization's chief on Friday.

The remarks by WHO Director-General Tedros Adhanom Ghebreyesus represent a shift in tone, coming just months after he stated that the world has never been in a better position to end the pandemic.

"We are much closer to being able to say that the pandemic's emergency phase is over, but we are not there yet," Tedros said on Friday.

The global health agency estimates that about 90% of the world's population now has some level of immunity to SARS-COV-2 either due to prior infection or vaccination.

"Gaps in testing ... and vaccination are continuing to create the perfect conditions for a new variant of concern to emerge that could cause significant mortality," Tedros said.

COVID-19 infections are at record highs in China and have started to rise in parts of Britain after months of decline.

Further easing of COVID-19 testing requirements and quarantine rules in some Chinese cities was met with a mix of relief and worry on Friday, as hundreds of millions await an expected shift in national virus policies after widespread social unrest.

"While COVID-19 and flu can be mild infections for many, we must remember that they can cause severe illness or even death for the most vulnerable in our communities," said Mary Ramsay, director of public health programs at the UK Health Security Agency.

The WHO urged governments worldwide to prioritize reaching out to those at risk for vaccination, such as those over the age of 60 and those with underlying conditions.