Police and fire authorities responded just before noon to a house fire in Grand Haven Township, on the eastern shore of Lake Michigan. When they went inside, they found the bodies, Capt. Jacob Sparks of the Ottawa County Sheriff's Office said at an evening news conference, CNN reported.
Sparks said authorities had not fully identified all the victims yet and do not have an official cause of death for them. The children's ages ranged from 5 to 15, he said.
He did not say how many of the people had gunshot wounds.
"It's a complicated scene, a complex scene," Sparks said.
He said investigators were not looking for outside suspects and one theory so far is a murder-suicide. He said everyone who lived in the home appeared to be deceased.
Sparks said the fire was "suspicious" and there was reason to believe it was intentionally set. Michigan State Police arson investigators are assisting on scene, he said.
Grand Haven Township has a population of about 18,000 and is 25 miles west of Grand Rapids.