New York state reported Friday that just over 21,000 people had tested positive for COVID-19 the previous day, the highest single-day total for new cases since testing became widely available.

One-day snapshots of virus statistics can be an unreliable way to measure trends, but the new record punctuated a steady increase that started in the western part of the state in late October, and has taken off in New York City in the past week as the omicron variant spreads.

“This is changing so quickly. The numbers are going up exponentially by day,” Gov. Kathy Hochul said during a Friday appearance on CNN.

A screen shows the cancellations of The Rockettes performance due to COVID-19 cases on Friday, Dec. 17, 2021, in New York.  New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)

A screen shows the cancellations of The Rockettes performance due to COVID-19 cases on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)

Just under half of the positive results were in the city, where lines were growing at testing stations and some Broadway shows and the Rockettes Christmas show were cancelling performances because of outbreaks among cast members.

The steep rise in infections should be of great concern but it was inevitable, given the quick spread of the newest variant, said Dr. Denis Nash, the executive director of the Institute for Implementation Science in Population Health at the City University of New York.

“We were already headed for a winter surge with delta, which is a very concerning thing in its own right,” Nash said.

People wait in line to get tested for COVID-19 at a mobile testing site in Times Square on Friday, Dec. 17, 2021, in New York.  New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days.(AP PhotoYuki Iwamura)

People wait in line to get tested for COVID-19 at a mobile testing site in Times Square on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days.(AP PhotoYuki Iwamura)

“But then you layer on top of that the new omicron variant, which is more transmissible from an infection standpoint,” he said, noting that current vaccines may be unable to contain the “more invasive” new variant.

Statewide, New York averaged 13,257 positive tests per day over the seven-day period that ended Thursday. That is up 71% from two weeks ago.

The state's previous one-day high for positive tests came on Jan. 14, 2021, when just under 20,000 people tested positive.

A person seen in silhouette gets tested for COVID-19 at a mobile testing site in Times Square on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)

A person seen in silhouette gets tested for COVID-19 at a mobile testing site in Times Square on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)

New York City Mayor Bill de Blasio has warned that omicron is in “full force," but said the city’s hospitals are “very strong and stable right now” and far better able to handle COVID-19 than when the pandemic began. Treatments have improved, and more than 70% of eligible city residents are fully vaccinated, he noted.

People wait in line to get tested for COVID-19 at CityMd near Central Park on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)

People wait in line to get tested for COVID-19 at CityMd near Central Park on Friday, Dec. 17, 2021, in New York. New York City had been mostly spared the worst of the big surge in COVID-19 cases that has taken place across the northeastern and midwestern U.S. since Thanksgiving, but the situation has been changing rapidly in recent days. (AP PhotoYuki Iwamura)