The city of New York has declared a public health emergency in response to the growing outbreak of measles in the Williamsburg section of Brooklyn, WLNY-TV reported Tuesday.

All unvaccinated adults and children who live or work in Williamsburg are ordered to receive an MMR (measles, mumps, and rubella) vaccine within 48 hours, New York Mayor Bill de Blasio and Health Commissioner Dr. Oxiris Barbot announced during a news conference Tuesday. Those who don't comply could face a $1,000 fine.

"Today we are declaring a public health emergency effective immediately. This will mandate vaccines for people living in the affected area," de Blasio said. "The Department of Health will issue violations and fines to people who remain unvaccinated.

"We have a very serious situation on our hands. We cannot allow this dangerous disease to make a comeback in New York City. We have to stop it now," he said. "The only way to stop this outbreak is to ensure that people who have not been vaccinated get the vaccine."

At least 285 confirmed cases of measles in Brooklyn and Queens have been reported since October, according to the New York City Health Department. Of those cases, at least 21 ended up hospitalized, WLNY reported.

"It's crucial for people to understand the measles vaccine works," de Blasio continued. "It is safe. It is effective. It is time tested."

The outbreak has mostly occurred within the Orthodox Jewish community where some parents have opted out of vaccinating their children citing religious reasons.

"There is no religious exemption on measles," Gary Schlesinger, CEO of Parcare Community Health Network, told WLNY. "All rabbis, all prominent rabbis have issued proclamations that everyone should vaccinate."

Schlesinger is working with the Orthodox community to reverse the spread of false messaging.

The vaccination mandate would remain in place until the New York City Board of Health's next meeting on April 17 when officials will determine whether or not to continue the order, Barbot said in the release.

What else did officials say?

Deputy Mayor for Health and Human Services Dr. Herminia Palacio echoed de Blasio's comments citing the safety and effectiveness of the MMR vaccine.

"Get the measles vaccine," Palacio said.

The infection can cause serious illness and complication in infants, pregnant women, and those compromised immune systems, she continued.

"I want to set the record straight. This vaccine is safe. This vaccine not only protects your child but it protects other people's children," she added.

She also urged parents to avoid the practice of "measles parties," which she said has contributed to the outbreak.

What about the nationwide outbreak?

A total of 465 cases across 19 states have been confirmed this year, according to the latest data from the U.S. Centers for Disease Control and Prevention.

Last year, there were 372 cases nationwide.

What else?

On Monday, city officials warned yeshiva schools in Brooklyn that they could be fined or shut down if they allow unvaccinated to children to attend school.

Late last month, Rockland County officials declared a 30-day state of emergency banning unvaccinated minors from public spaces.

The county has seen 168 confirmed cases since October, according to health officials.