Route 1 has reopened after firefighters spent most of the night fighting a three-alarm fire  in Scarborough.

The fire heavily damaged a commercial building at 153 Route 1 across the street from Lois’ Natural Marketplace.

Additional Photos

Members of State Fire Marshall office and ATF begin investigation of last nights fire at Scarborough Commons Tuesday. John Patriquin/Staff Photographer

Members of the state Fire Marshal's Office and federal Bureau of Alcohol, Tobacco, Firearms and Explosives begin investigation of Monday night's fire at Scarborough Commons Tuesday. John Patriquin / Staff Photographer

Firefighters spray water from above the flames at the Scarborough Commons building on Route 1 Monday night. Shawn Patrick Ouellette/Staff Photographer

Firefighters battle a three-alarm fire Monday night at the Scarborough Commons commercial building at 153 Route 1. Shawn Patrick Ouellette/Staff Photographer

Firefighters were still dousing flare ups at 4 a.m. but by 5 a.m., Route 1 between Maple Avenue and Portland Farms Road had reopened, according to the Scarborough Fire Department’s Facebook page.

After spending six hours battling the fire at Scarborough Commons, which destroyed many of the 18 offices and studios there, Scarborough firefighters assisted the Saco Fire Department at a fully involved barn fire.

The State Fire Marshal’s Office has been called in to investigate the cause of the Scarborough Commons fire.

The fire, which was under control but still flaring up late Monday night, affected about 18 tenants in Scarborough Commons, including a yoga studio, a hair salon, a legal center, a massage therapist and a doctor’s office.

Many of the offices and studios were destroyed by the fire.

The structure was built in phases, which made it difficult for fire crews to attack.

“It spread pretty rapidly because of the size of the building,” Capt. Jim Butler of the Scarborough Fire Department told WCSH-TV.

Firefighters from five neighboring communities assisted Scarborough in battling the blaze.

Route 1 from Hannaford Drive north to the Maine Medical Center campus near the South Portland city line remained closed and may not reopen until Tuesday morning, police said.

No serious injuries were reported, but WCSH-TV said three Scarborough firefighters were taken to a hospital for treatment of heat exhaustion.

“I’m in total shock,” said Richard Aube, the owner of Scarborough Commons.

The complex is at 153 Route 1, across the street from Lois’ Natural Marketplace, a natural foods store, and Route 1’s intersection with Portland Farms Road.

Scarborough police said on its Facebook page that fire crews from Cape Elizabeth, Gorham, Portland, South Portland and Westbrook responded to the fire, which was reported at 7:41 p.m.

A fire dispatcher described the damage as extensive.

Investigators from the State Fire Marshal’s Office were called in and will try to determine a cause of the fire.