A day before it was reportedly slated to have its fire systems inspected, a nearly completed 83-unit mixed-use building in Boston went up in flames.

Located in the Ashmont section of the city’s Dorchester neighborhood, the $45-million wood-framed building called the Treadmark had fire sprinklers installed but they were not yet activated. The six-alarm blaze that began around 2 p.m. on June 28 didn’t cause any major injuries. One construction worker was treated for chest pains.  

Thick smoke billowing from the six-story building shutdown streets the entire night as crews continued to put out hot spots. Firefighters didn’t enter the building as the roof was in danger of collapsing. 

“Will be unable to enter building until at least late tomorrow afternoon - if safe to do,” the Fire Dept. tweeted at 9:35 p.m. “Too early to determine cause.”

The Boston Herald reported that two workers on the scene said a generator on the roof caught fire while testing systems that power emergency exit signs and lighting. 

Fire Commissioner Joe Finn tweeted at 12:02 a.m., “Thanks to our firefighters for the effort in a most difficult fire Wednesday. Always tough when doing exterior operations.”

The building featured several affordable-housing units and was slated to open next month. Thirty condos were already sold, many apartments were already rented and a business was set to move into the first floor. The developer, Jim Keefe of Trinity Financial, vowed to rebuild. 

“We care deeply about the Ashmont neighborhood and are heartbroken,” he said in a statement. “The most important thing is that no one was seriously hurt. … We are fully committed to making sure this project gets rebuilt as quickly as possible.”