Several firefighters were injured battling a stubborn six alarm blaze that has been raging in the basement of a Flatiron District building for more than nine hours, the FDNY said.

The fire started in the boiler room of a five story building on West 29th Street near Fifth Avenue shortly after 1 a.m.

Firefighters arrived on scene and began battling the flames, which are “deep-seated” and “tough to reach” according to an FDNY spokesman.

Six firefighters had to be taken to Bellevue Hospital for minor injuries, which mostly included heat exhaustion and smoke inhalation.

The fire was still not under control as of 10 a.m., officials said.

The cause of the fire is unknown.