A 4-year-old boy has died after being struck by a vehicle that then left the area, Boston police said.

An off-duty firefighter was the first on the scene to provide aid to the child after he was struck in the city's Hyde Park neighborhood at about 9:30 p.m. Tuesday. Emergency medical services transported him to a hospital, where he was pronounced dead, police said.

No names were made public.

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Mayor Michelle Wu called the death a "horrible tragedy."

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"It’s absolutely devastating to think about what transpired in just a split-second," she said at a news conference at the scene late Tuesday.

Police are looking for surveillance video from the area and seeking witnesses.

"If anyone saw or heard, or knows anything with regards to what happened here tonight, please let us know," Suffolk District Attorney Kevin Hayden said at the scene. "We beg of you. We need your help."