A fire that raced through a Washington Street apartment building displaced 30 residents but caused no injuries, the Boston Fire Department reports.

The fire at 247-249 Washington St. was reported around 7:05 a.m. and did an estimated $750,000 in damage, the department says.

The department blames "careless disposal of smoking material" on a rear porch for the fire.

Firefighters arrived to find flames showing from rear porches, the depatment says, adding the cause remains under investigation.