Mayor Bill de Blasio declared a public health emergency on Tuesday and has ordered mandatory vaccinations for people who may have been exposed to the virus in parts of Williamsburg amid a growing measles outbreak.

Since September, the city said more than 250 measles cases have been confirmed in the Brooklyn neighborhood.

"We have a situation now where children are in danger. We have to take this seriously. Every one of us has to feel responsibility for the situation because measles is so contagious, can spread so quickly," de Blasio said at news conference at a Williamsburg library on Tuesday morning.

Under the order, unvaccinated people, including children over 6 months old, who live or work within zip codes 11205, 11206, 11221 and 11249 will be required to get an MMR vaccine.

Members of the city's Health Department will check the vaccination records of any individual who may have been in contact with infected patients.

Those who have not received the vaccine or do not have evidence of immunity may be given a violation and could be fined $1,000.

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

The order will remain in effect through April 17. The city's Board of Health will then decide whether to extend or rescind the order.

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