The simultaneous circulation of the Delta and Omicron variants of the coronavirus is creating a "tsunami of cases", World Health Organisation (WHO) director-general Tedros Adhanom Ghebreyesus told a news briefing.

"Delta and Omicron are now twin threats driving up cases to record numbers, leading to spikes in hospitalisations and deaths," said Tedros.

"I am highly concerned that Omicron, being highly transmissible and spreading at the same time as Delta, is leading to a tsunami of cases."