New York's daily rate of positive coronavirus tests climbed to 3.25 percent over the last 24 hours, with a sharp increase in cases among Orthodox Jewish communities, authorities said Tuesday.

The elevated rate, which was at 1.93 percent just the day before, marks a worrisome step for a city that has made drastic progress in fighting the coronavirus.

New York City, where more than 23,800 people have died of coronavirus, became the global epicenter of the pandemic in spring but has recently touted some of the lowest test positivity rates and infection rates among major US cities.

"For the first time in quite a while, the daily number is over three percent and that is cause for real concern," Mayor Bill de Blasio told reporters, announcing that the city would begin fining those not wearing masks in public.

The increase in cases occurs in the same week that hundreds of thousands of children return to in-person school.

It also comes as restaurants and bars will begin allowing indoor dining at 25 percent capacity for the first time since March starting Wednesday.

New York Governor Andrew Cuomo blamed the rise on "a lack of compliance" and said that 20 state zip codes, all with a strong Orthodox Jewish populations, have daily test positivity rates that average five percent.

Rockland County zip code has a 30 percent rate, he said.

Cuomo said he will meet virtually with Orthodox Jewish leaders and local elected officials from the communities most affected by the coronavirus to insist on the need to abide by the rules.

The governor admitted he was nervous about public school reopening, which is scheduled for Thursday.

Mayor De Blasio said that schools would close again if the daily test positivity rate is higher than three percent for seven days.