Somerville firefighters fought a blaze at a Union Square bakery Wednesday night.

The fire broke out in the basement of Fiesta Bakery & Restaurant, at 316 Somerville Ave. at about 7 p.m., according to scanner reports.

Boston.com reported that one firefighter was injured in the incident and transported to Massachusetts General Hospital with unknown injuries.

Breaking News Network, a notification service that monitors police, fire and first-responder scanner transmissions, reported firefighters knocked down ceilings and walls in the building and sought immediate assistance from the gas company to deal with a gas leak. The notification service reported the fire was mostly in the walls and ceiling.

One witness, Katie Lannigan, a former Somerville Patch correspondent, reported traffic was shut down near the area as fire companies battled the blaze. Police closed off Somerville Avenue back to School Street.

Firefighters had substantially put out the fire by 8 p.m.

Daniel DeMaina contributed to this report.