The 3-alarm blaze broke out in the Hunter Hills complex on North Main Street just after 9:15 p.m., according to initial reports and confirmed by several responding fire departments on social media.
Two borough police officers were first at the scene to evacuate all residents as first responders arrived to prevent further spreading of the fire.
One resident was airlifted to a local hospital for treatment of burns, Flemington borough officials said.
The Flemington-Raritan First Aid and Rescue Squad also responded to the scene.
A dozen apartment units were damaged in the blaze, and the Red Cross, council, Mayor and OEM are working with those who have been displaced.
Other assisting agencies include the Clinton Fire Department and the Quakertown Fire Company.
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