NEW YORK (AP) — Museums prepared to shut their doors, the opera was silenced, lights dimmed on Broadway, big gatherings were banned and the subway was shunned as the largest city in the United States wound down Thursday amid a rise in coronavirus cases.

Gov. Andrew Cuomo announced that gatherings with more than 500 people will temporarily be banned in New York state, one of several “dramatic actions” to contain the new virus.

The governor said the ban would start for most places statewide at 5 p.m. Friday, though he said it does not apply to schools, hospitals, nursing homes and mass transit. Cuomo said it would be “tremendously disruptive” to close schools en masse. He gave broad outlines of plans to reduce “sustained close contact,” including a requirement to reduce crowding at smaller events, but offered few details.

The ban for Broadway theaters started at 5 p.m. Thursday. Producers said they hoped to resume shows on April 13, according to a statement from The Broadway League, an organization of theater owners and producers.

“The last 24 hours have been very, very sobering,” said New York City Mayor Bill de Blasio at a separate briefing later Thursday. The mayor declared a state of emergency for the city.

Cuomo said the city has 95 confirmed COVID-19 cases as of Thursday afternoon. There are more than 320 cases statewide, with the largest cluster in the suburb of New Rochelle north of New York City. De Blasio predicted the city could be at 1,000 cases by next week and said the crisis could last six months or longer.

The ban comes as some of New York City's most esteemed cultural institutions announced Thursday they are temporarily shutting down because of the coronavirus, including the Metropolitan Museum of Art, the Museum of Natural History, the Metropolitan Opera and Carnegie Hall.

“The Met’s priority is to protect and support our staff, volunteers, and visitors,” Daniel Weiss, the Metropolitan Museum's president and chief executive, said in a statement. The museum will close its three locations starting Friday. No date for reopening was given.

The opera company said all performances have been canceled through March 31. Carnegie Hall also announced it was closing its doors at midnight Thursday for all public events through the end of March.

The cascade of closings left some tourists shaking their heads in disbelief. Ken and Theresa Winter, visiting from Colorado, headed to Broadway on Thursday after the Big East basketball tournament was hastily scrapped.

Theresa Winter said the reaction to the coronavirus reminded her of the uncertain days following the Sept. 11 attacks. She noted their plane to New York City was less than half full.

“Hopefully we can get back to Denver,” she said.

The closings come amid signs that New Yorkers are acting on their own to avoid crowds. Ridership on the subway and commuter rail lines has plunged, state officials said.

Cuomo announced late Wednesday that New York City's St. Patrick's Day Parade would be postponed for the first time in its 258-year history. De Blasio later tweeted that the parade will take place at some future date “whether it’s in the heat of summer or on a clear fall day."

The virus causes only mild or moderate symptoms such as fever and cough for most people, but for some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.

The vast majority of people recover. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three to six weeks to recover.

The Archdiocese of New York said it will close elementary schools in its system Monday for at least a week.

De Blasio said in a statement that two public schools that share a building in the Bronx will close for 24 hours because a student tested positive for COVID-19.

But the mayor said he hopes to avoid drastic measures, such as shutting the city's entire public school system or its subways. He said health care workers and first responders on the front lines of the crisis would face hurdles in getting to work without the transit system and with children home from school.

“Our greatest concern has been how to balance all these factors and insure that we could keep a functioning society,” de Blasio said.

North of the city in hard-hit New Rochelle, camouflage-clad National Guard troops helped distribute food to residents Thursday.

State officials this week set up a "containment area" in the suburb in which schools and houses of worship are closed within a mile radius of a point near a synagogue associated with the cluster. People who aren't personally quarantined will be able to leave their homes and go to work or elsewhere. Businesses can remain open, and residents or visitors are free to walk around.

The Cuomo administration did not say how many troops were mobilized.

Though cases were concentrated in the New York City area, confirmations were reported in new parts of the state. Officials in Rochester said the first known case in western New York involved a man who had visited Italy. The University at Albany suspended classes Thursday after a student tested positive for COVID-19, one of two new cases in the county.

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Associated Press writers Marina Villeneuve and Mary Esch contributed from Albany, N.Y.

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