PORTLAND — An early morning fire Saturday did between $5 million and $9 million worth of damage to a historic island fort property being renovated as a hotel.

According to an announcement Saturday morning by Deputy Portland City Manager Sheila Hill-Christian, the Portland Fire Department responded to a structure fire at 18 McKinley Court on Great Diamond Island at approximately 4:30 a.m.

The fire was reported by the Casco Bay Bridge tender who reported seeing a glow from the island, she said after an 11 a.m. press conference at Portland City Hall.

The Inn at Diamond Cove, a project under construction, was found ablaze, Hill-Christian stated.

“The Inn at Diamond Cove is being developed in a former U.S. Army Barracks on the Fort McKinley site on Great Diamond Island,” she wrote in her morning announcement. “It is a reuse of the last, and largest, building on the complex into a full-service hotel with a variety of room types. This site is on the National Register of Historic Places.”

Firefighters and police officers from Portland and Long Island joined island volunteers at the scene. Fire personnel were still at the scene as of 12:30 p.m. Saturday, although Hill-Christian said the blaze was under control and no injuries were reported. She described the damage as being worth between $5 million and $9 million to the historic property in a press release issued about 12:30 p.m..

“Due to the magnitude and location of the fire, we have requested and received approval for the State Fire Marshal’s office to assist in the investigation,” said Deputy Portland Fire Chief Robert Wassick in a statement. “This is routine under these circumstances.”

The State Fire Marshal’s Office will provide periodic updates regarding the investigation, Hill-Christian said in the afternoon press release.

Fire Marshal Sgt. Joel Davis said in the release that getting heavy equipment out to the island would be a challenge in the investigation. The equipment will be needed to move heavy debris in order to fully evaluate evidence at the scene, the press release said.

The city of Portland acquired the historic barracks property in 2005 due to unpaid taxes and agreed to turn it over to hotel developers four years later for $1. A group of Great Diamond Island residents protested the hotel project, arguing the new influx of transient visitors would disrupt the island’s neighborhood atmosphere.

Jeff Levine, director of Planning and Urban Development for the city, said at the press conference that “this project is a wonderful reuse of a long abandoned property. While the future status of this project is now unknown, we remain optimistic with regard to development of the site.”