NEW YORK — On the corner of Bedford and Division avenues in Brooklyn, in the heart of the New York borough’s Orthodox Jewish community, men in black hats and suits rushed in and out of cafes and women with headscarves pushed strollers or carts filled with groceries, not eager to speak with an outsider.

There was little indication that the Williamsburg neighborhood was the center of the nation’s biggest outbreak of measles, a once eradicated disease that has returned as some parents shun the vaccines that killed it off. On Tuesday, the 285 cases reported in the borough prompted Mayor Bill de Blasio to declare a public health emergency, allowing him to impose $1,000 fines – or even jail time – on those who haven’t been inoculated and shining a light on the small, insular religious circles where the virus has spread.

“No one I know has measles, my dad’s a doctor and none of his patients have measles,” said Avi Rose, 17, who’s been vaccinated and assumes that almost everyone else he knows has been, too. Of the city’s order focusing on the tightly knit neighborhood, he said, “I think it’s not going to happen. Most people are vaccinated. They can’t enforce it.”

Such outbreaks have made an alarming, if limited, comeback since the turn of the century, when they had disappeared from the country. The return came amid concern among parents that vaccines are connected to health issues such as autism, despite a lack of scientific evidence and the consistent effort of medical experts to dislodge such beliefs.

There were as many as 667 cases of measles in 2014, according to the Centers for Disease Control and Prevention. Infections have been confirmed in 19 states this year. Nowhere has been more affected than Brooklyn and Rockland County, northwest of New York City. The two account for more than half the 465 U.S. cases reported this year as of April 4.

Gov. Andrew Cuomo, a Democrat who has frequently sparred with de Blasio, said the mayor’s action is likely to raise questions about freedom of religion, noting that New York law allows exceptions to vaccinations based on such beliefs. But state Sen. Brad Hoylman has moved to strike that provision when it comes to school-age children, pointing to similar legislation enacted by California.

“The First Amendment’s freedom of religion doesn’t give you the right to endanger other people’s children and your own,” Hoylman, a Manhattan Democrat, said in an interview. “It’s well-documented that people use this as a loophole to resist vaccination based on their own notions of bunk science.”

Not everyone sees it that way. Robert Krakow, a New York lawyer representing people who allege injury from vaccines, said he’s preparing a lawsuit claiming the city overstepped its powers. And in interviews with local residents on Wednesday, there was also skepticism about the mayor’s order from those outside the Orthodox community.

Todd Barone, 40, a high school administrator, said he and his wife were undecided about their son receiving all of the recommended vaccines. “We don’t know if all the vaccinations are necessary,” he said in Williamsburg. “At the same time, you have to trust your doctor.”

Dorit Rubenstein Reiss, a law professor at the University of California’s Hastings College of the Law in San Francisco who specializes in vaccine policy, said the religious exemptions arise when children enter school and wouldn’t stop the city from removing them in the middle of an outbreak.

“The question arises, is this a religiously targeted law,” she said. “In order to prevail, the city’s policy must have a demonstrable rational basis. The city’s argument here is ‘we aren’t targeting your religion, we’re targeting disease.’ The question also becomes, is this the least restrictive or least onerous alternative?”

In Rockland County, anti-vaccination advocates last week persuaded a judge to rule that officials overstepped their authority by ordering some schools to bar unvaccinated students and banning other children from “places of public assembly.” The judge ruled the outbreak wasn’t enough of an emergency to justify those steps, a decision that county officials said they intend to appeal.

New York City declared its state of emergency after officials spent months unsuccessfully working to quell an outbreak of the infection, including by working with rabbis who were seeking to dispel concern about vaccines. De Blasio said the city acted this week to prevent the virus from spreading when families gather for the Passover holiday this month. He said those who haven’t received the vaccine or don’t have evidence of immunity will be given an opportunity to get vaccinated before being hit with a violation.

The power of governments to require vaccination has been established law since 1905, when Henning Jacobson, a Protestant minister in Cambridge, Mass., defied a local Board of Health order requiring adults to get smallpox vaccinations or pay a $5 fine. In that case, the U.S. Supreme Court held that the state can limit individual rights to support a public health necessity.

Yet the law also requires that measures be reasonable – and not excessive or harmful when gauged against the broader benefits to society, said Wendy Parmet, a law professor and director of Northeastern University’s Program on Health Policy and the Law.

In Philadelphia, a 1991 measles outbreak afflicted hundreds of children, including several fatally, in a school of 1,000 students run by the Faith Tabernacle Congregation, an insular Christian sect, raising alarm among city health department officials who obtained a court order forcing parents to have their children vaccinated.

“The city might have a problem with this beyond the mere issue of state law allowing religious exemptions,” Parmet said. “When public health authorities act in a crude, blunt way on vaccines, that can be counterproductive. You can’t forcibly vaccinate people, so you’ve got to get to a place where parents come around and want their kids vaccinated. Sometimes a rush to emergency powers is unwise.”