NEW YORK (NYTIMES) - With more than 580,000 cases, the United States shattered its own record for new daily coronavirus cases on Thursday (Dec 30), beating a milestone it already broke just the day before.

Thursday's count, according to The New York Times' database, toppled the 488,000 new cases on Wednesday, which was nearly double the highest numbers from last winter.

The back-to-back record-breaking days are a growing sign of the virus's fast spread and come as the world enters its third year of the pandemic.

Hospitalisations and deaths, however, have not followed the same dramatic increase, further indication that the Omicron variant seems to be milder than Delta and causes fewer cases of severe illness.

Across the country, airlines cancelled thousands of flights, leaving would-be travellers stranded, while others waited in line for hours to get their hands on a coronavirus test.

The high numbers are even more striking considering that experts associate the holiday season with major disturbances in testing and data reporting.

The rise of at-home tests could also mean some cases aren't making into the official count.

Last year, the so-called holiday curve showed a major decline in cases after Thanksgiving and Christmas, which under-reported the spike in cases that actually took place.

It's likely that this season many more people have the virus than what's being accounted for; just how many may not be clear for another few weeks.

The worldwide surge is being propelled by the new variant, Omicron. And while it is more infectious, research shows that cases with the variant are milder.

Vaccinations are already proven to reduce the severity of the virus.

The majority of Americans, 62 per cent, are fully vaccinated, according to The New York Times's database.

Nearly three-quarters of people have received at least one dose. And 68.8 million of those fully vaccinated have also received a third dose, or booster shot, since Aug 13, according to the Centres for Disease Control and Prevention.