Firefighters are battling a three-alarm blaze that has gutted affordable housing complex under construction at 2700 Middlefield Road in North Fair Oaks.

The building is in unincorporated San Mateo County near Costco and the Redwood City limits.

Nobody is inside the building and firefighters are taking a “defensive” posture, pouring water on the fire but not trying to go inside the building, according to the Menlo Park Fire Protection District, which responded along with Redwood City firefighters.