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NEW: Fire department says 1 person suffers "serious head injury"; another has minor injury

33-story residential high-rise was under construction in downtown Boston

The collapse affected the 12th through fifth floors

CNN  — 

A building under construction in downtown Boston partially collapsed Thursday morning, sending two people to the hospital, the city’s fire department said.

The incident happened about 8 a.m. at a construction site at 45 Stuart St., the Boston Fire Department tweeted.

The collapse occurred on the 12th floor of what’s slated to be a 33-story residential high-rise, causing damage from the 11th floor’s roof down to the fifth floor.

First responders treated two people with injuries that were not life-threatening and then took them to nearby Tufts Medical Center. The fire department later explained that one of those had “a serious head injury,” while the other had a minor injury.

“No others workers reported trapped at this time,” the fire department tweeted.

According to a sign posted outside the site, near the city’s Chinatown district and around the corner from Boston Common, the building was slated to be completed in the middle of next year.