New York City Mayor Bill de Blasio declared a health emergency in areas of Brooklyn on Tuesday and ordered mandatory vaccinations for those who may have been exposed to the measles virus.

The order covers people who live in four ZIP codes in the Williamsburg neighborhood of Brooklyn, where more than 250 people have contracted measles since September.

YESHIVA SCHOOLS ORDERED TO EXCLUDE UNVACCINATED STUDENTS AMID MEASLES SURGE

The order requires all unvaccinated people in those areas who may have been exposed to the virus to get vaccinated, including children older than 6 months. Those who didn’t get the vaccine or are not immune to the virus may be fined $1,000.

“There’s no question that vaccines are safe, effective and life-saving,” de Blasio said in the news release. “I urge everyone, especially those in affected areas, to get their MMR vaccines to protect their children, families and communities.”

Health commissioner Dr. Oxiris Barbot blamed those against vaccines for causing the outbreak.

“As a pediatrician, I know the MMR vaccine is safe and effective. This outbreak is being fueled by a small group of anti-vaxxers in these neighborhoods. They have been spreading dangerous misinformation based on fake science,” he said in the news release. “We stand with the majority of people in this community who have worked hard to protect their children and those at risk. We’ve seen a large increase in the number of people vaccinated in these neighborhoods, but as Passover approaches, we need to do all we can to ensure more people get the vaccine.”

The New York City Health Department on Monday ordered all ultra-Orthodox Jewish schools in the Williamsburg neighborhood to exclude unvaccinated students from during the measles outbreak.

Any yeshiva in Williamsburg that doesn’t comply with the order will face fines and possible closure, the health department said.

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New York City accounted for about two-thirds of all U.S. measles cases reported last week, according to the Associated Press.

The Associated Press contributed to this report.