Fire destroyed a family-owned houseboat rental business on Rainy Lake in northern Minnesota, killing an 85-year-old woman and injuring her daughter and another family member, officials said Thursday.

The blaze broke out about 5:10 p.m. Wednesday at Northernaire Houseboats on Jackfish Bay, about 7 miles east of International Falls, according to the Koochiching County Emergency Operations Center.

Firefighters arrived and saw the business' main office and other space "fully engulfed," an emergency services statement read. The destroyed property included the business owners' home, said Operations Center spokeswoman Valerie Marasco Eliasen.

A portion of the building was an older log structure, making the fire "hot and difficult to battle," an Operations Center statement read.

The body of Lavonne S. Hershberger was recovered from the charred debris about 11:20 p.m. Wednesday, Eliasen said. Her critically injured 51-year-old daughter and business co-owner, Vonnette L. Mills, was taken by air ambulance to a trauma hospital, while a 12-year-old girl, also a family member, was at International Falls' Rainy Lake Medical Center in stable condition.

The blaze was nearly out about 3¼ hours after it began, the Operations Center statement continued. Fire crews stayed on the scene until about 3 a.m. Thursday. Six firefighters suffered heat exhaustion but were not admitted to the hospital.

Officials have yet to say how the fire started, "but early signs point to it being accidental in nature, and there is nothing suspicious at this time," a statement from the Operations Center read.

Northernaire was taken over in 2019 by Kevin and Vonnette Mills. In a notice posted Thursday on Facebook, its operators wrote that the fire has forced them to close for the season, but they vowed to reopen at some point.

"Thank you for giving the Northernaire Houseboats crew some time and space to process yesterday's fire," the posting read. "​We thank you for the outpouring of support and prayers."

Eliasen said that "this community has been through so much this spring and summer between the historic flooding, a freak boating accident a few weeks ago injuring two local gentlemen and now this fire wiping out the home and business of Northernaire Houseboats, a longtime business of International Falls."

She added that the incident was "difficult for emergency responders in small communities when the victims are known to each other. [It was] a very tough night for all involved."