WHO's director-general said a wave of COVID-19 cases would strain already stressed hospital systems.

He said he was concerned that Omicron cases were rising while the Delta variant remained prevalent.

The World Health Organization's warning comes as the US is experiencing a surge in infections.

The head of the World Health Organization said a "tsunami" of COVID-19 cases driven by the Omicron variant would pressure hospital systems already on the "brink of collapse."

"I am highly concerned that Omicron, being more transmissible, circulating at the same time as Delta, is leading to a tsunami of cases," WHO Director-General Tedros Adhanom Ghebreyesus said on Tuesday. "This is and will continue to put immense pressure on exhausted health workers and health systems on the brink of collapse."

What to know about rapid at-home COVID tests as cases surge
His warning comes as the US is in the middle of a surge of new COVID-19 infections. On Monday, the country reported more than 440,000 new COVID-19 infections in one day, shattering the record set in January.

While that figure may be abnormally high because of slower reporting over the holiday weekend, the seven-day average of new COVID-19 cases is also on track to break a pandemic record, according to data from the Centers for Disease Control and Prevention.

The CDC estimated the Omicron variant represented almost 60% of all cases in the US last week.