Lapses in strategies to tackle COVID-19 this year continue to create the perfect conditions for a deadly new variant to emerge, as parts of China witness a rise in infections, the head of the World Health Organization said on Friday.

The comments by WHO Director-General Tedros Adhanom Ghebreyesus mark a change in tone just months after he said 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 emergency phase of the pandemic is over, but we're 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 not forget that they can cause severe illness or even death for those most vulnerable in our communities", Mary Ramsay, director of public health programmes at the UK Health Security Agency, said.

The WHO urged governments globally to focus on reaching those at risk, such as people over the age of 60 and those with underlying conditions, for vaccination.