The electrical fire broke out in the building on East 54th Street just after 6:15 a.m.
Elevated carbon monoxide levels were detected in up to four buildings, one of them residential.
The buildings were ventilated, and the carbon monoxide levels have since dropped.
Four people suffered non-life threatening injuries.
East 54th Street was closed to vehicular traffic between Park Avenue and Lexington Avenue.
The cause of the fire is not yet known, and the investigation is ongoing.
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