A three-alarm fire in a six-family three decker at 4 Theodore St. Saturday night sent two residents and two firefighters to the hospital.

The fire, reported at 10 p.m., started in a first-floor bedroom, but did heavy damage to the second and third floors, the Boston Fire Department reports. One of the residents suffered burns; the firefighters were hurt when a chimney collapsed, the department says.

At least 20 people were made homeless, by the fire, which fire officials estimate caused $400,00 in damage. The cause is still under investigation.