A 39-year-old gunman killed five people and then himself in a series of killings on Friday in the US state of Michigan, state police said.

Police said in a statement that officers were responding to reports of a shooting at a home in Missaukee County at about 11:40 a.m. local time (1540 GMT), when they found three people dead and another critically injured.

The suspect, Chad Hickman, had fled the scene before law enforcement arrived, prompting a "large-scale" manhunt, police said, adding that during the search, they found a fourth person dead at another home.

Hickman's vehicle was spotted near Whitlock Lake in Caldwell Township, leading officers to his body and another dead person in the woods, police said.

A motive for the killings was not immediately known. Authorities said an investigation is underway.