The mayor's office declared a public health emergency Tuesday in specific areas of Williamsburg where a measles outbreak is affecting the Orthodox Jewish community.

It means that anyone who is not vaccinated and living in the area who might have been exposed to the measles will be required to receive the vaccination.

Mayor Bill de Blasio says measles is a dangerous and potentially deadly illness, that can easily be prevented with a vaccine.

The city is calling on everyone living in ZIP codes 11205 11206 11211 and 11249 to get the measles, mumps, rubella (MMR) vaccine if they haven't already.

According to the city's health commissioner, nearly 300 cases have been confirmed since the beginning of the outbreak in October. That includes more than 20 hospitalizations and a handful of admissions to intensive care units.

There have been no deaths so far.

"It is crucial for people to understand that [the] measles vaccine works, it is safe, it is effective, it is time-tested," said Commissioner Dr. Oxiris Barbot.

The Health Department also warned against parents throwing “measles parties” as a way of infecting unvaccinated kids.

Those who have not been vaccinated or do not have evidence of immunity could be fined $1,000.

Anyone looking to find out where they can get vaccinated or to get more information can call 311.