A “significant fire” broke out on the 20th floor of the 43-story high-rise under construction in Haymarket Square Friday, triggering a five-alarm response by Boston firefighters and injuring two construction workers, officials said.
The high-rise is part of the Bulfinch Crossing development, the same project where engineers working for developer HYM Investment Group discovered structural issues with columns underneath the Government Center Garage that forced the MBTA to halt Green and Orange line service through downtown Boston.
Shuttle buses are in use and the T said it does not know when subway service will be restored.
Firefighters responded to One Congress Street mid-morning where smoke could be seen billowing out of the upper levels of the glass-enclosed building destined to be the headquarters for State Street Financial and InterSystems.
Deputy Chief James Greene said arriving firefighters discovered a “significant fire” on the 20th floor and that as many as 400 construction workers were in the building at the time. Workers were also on the 20th floor where the fire was discovered, he said.
“They are all accounted for,” he said. “We had two people, two construction workers who were evaluated by EMS, no serious injuries.”
The fire is out and the cause remains under investigation, Greene said.
Some fire crews were still on scene Friday afternoon, while construction workers gathered outside Boston Municipal Court where they had been evacuated by firefighters.
Annisha Simpson, a carpenter with the Local 328, was on the 32nd floor when she was alerted to the fire by a coworker. She said she and her coworkers thought it would be containable because there are fire extinguishers on every floor.
Two minutes later, she heard three air horn blasts and knew it was time to evacuate.
“As soon as we heard that, everyone started flooding the stairways, and everybody came down,” said Simpson, 28, of Dorchester. “When we came down to at least like [floor] 24, that’s when we started to smell the smoke. It was getting a little foggy, but not too much where people couldn’t breathe or couldn’t see.”
Jon Rubin, who works in telecommunications and is a member of Local 103, said he was on the 20th floor before the fire broke out. He said he heard sirens and people blowing the emergency horn.
Rubin, 22, hadn’t heard when the building would reopen. His keys and his wallet were still upstairs, he said.
The fire produced heavy smoke which was trapped inside the building on floors where windows — that cannot be opened — have been installed, he said. Firefighters had to break windows on some floors to allow smoke to escape the building.
“The fire is out. There is considerable overhaul to be done, a lot of trapped smoke and then an investigation to be done,” Greene told reporters.
Greene said sprinklers already installed in the building did activate, but the primary firefighting was performed by the department who used a construction elevator to move hoses near the fire scene on the 20th floor.
State Police closed off ramps from Interstate 93 at Congress Street in both directions due to the firefighting response.
John R. Ellement of the Globe Staff contributed to this report.