A bonfire in a Minnesota neighborhood meant to celebrate the long weekend broke out after an unknown flammable liquid caused exploding flames, killing one man and burning and injuring others.

A 53-year-old man died Friday evening from his injuries and a child who suffered severe burns was flown by helicopter to a hospital in Minnesota’s Twin Cities, county officials said.

A total of eight children and adults suffered burns and inhalation injuries from the fire in French Township, a small lakeside community about 90 miles (145 kilometers) northwest of Duluth.

The St. Louis County Sheriff’s Office said the flammable liquid used to start the fire was unknown. An investigation is ongoing.