New York City public schools are closing Thursday and returning to remote learning for all 1.1 million students because of rising coronavirus infection rates, Mayor Bill de Blasio (D) announced Wednesday. The city joins a rising wave of school closures around the country which are causing new disruptions to the tumultuous 2020-21 academic year.

In a separate announcement, Kentucky Gov. Andy Beshear (D) became the first governor to announce a statewide school closure, saying that all public and private schools must close Nov. 23 and that all public universities must do the same. Middle and high schools are staying shut until Jan. 4, and only elementary schools in areas without soaring infections will be allowed to reopen Dec. 7.

The closings of the largest school district in the country and all Kentucky schools are serious setbacks for state and local officials who had struggled to reopen schools and their communities during the pandemic, and the moves were certain to fuel concerns among educators and health experts about learning loss and the mental and social effects on children forced to stay home for months.

“School closures disrupt the lives of children and the capacity of parents to work, and have a particularly devastating impact on the most vulnerable populations of students, such as students with special needs, students living in temporary housing, and English-language learners," Jennifer March, executive director of the New York nonprofit Citizens’ Committee for Children, said in a statement. “These challenges are compounded by the fact that many households across New York City still lack remote learning devices, access to WiFi, cellular data service, or adequate technological support needed for successful remote engagement.”

There have been calls for officials to close other establishments first and keep schools open as long as possible — as is happening in European countries. But officials are making the call to close — or keep closed — schools to try to contain the spread of the coronavirus.

In Texas, Utah, Michigan, Georgia, Indiana and other states, some districts are temporarily closing schools that already opened, often because of pandemic-caused staffing shortages. In other places, including Chicago, Philadelphia, Boston, San Diego, Sacramento, Minneapolis and Topeka, Kan., districts have put off plans to reopen school buildings for the first time this academic year.

De Blasio (D) had warned for months that New York schools would close if the city’s coronavirus infection rate rose to 3 percent on a seven-day rolling average. On Wednesday afternoon, he announced his decision to close at a news conference after tweeting:

New York City has reached the 3% testing positivity 7-day average threshold. Unfortunately, this means public school buildings will be closed as of tomorrow, Thursday Nov. 19, out an abundance of caution.

Coronavirus rates are the highest they have been since the spring. Some governors are issuing stay-at-home orders and mask mandates, and Americans are being urged by health experts to stay home for Thanksgiving and not hold traditionally large gatherings. With the overall covid-19 death toll near 250,000, some health systems are overwhelmed.

While coronavirus infection rates have been rising in many communities overall, available evidence shows that virus transmissions in schools so far have not been significant. When de Blasio last Friday warned that the coronavirus positivity rate had hit 2.83 percent, the transmission rate in New York City schools was only 0.16 percent.

But in a message that has been repeated in other places, New York City Schools Chancellor Richard A. Carranza said in a tweet Wednesday that “health and safety have always been our first priority” for students, staff and families.

On Wednesday, New York City teachers in school buildings were told that all classes were switching to remote learning Thursday and that they should take home what they would need, according to the union that represents them.