Two toddlers are in a critical condition in hospital after a playmate accidentally shot them with a loaded gun at a daycare in the US state of Michigan.

Police in the Detroit suburb of Dearborn said the child managed to get a hold of a loaded gun inside a private home that functioned as a daycare.

The toddler fired either one or two shots that struck two children, both three years old, according to US media, which also reported that there were multiple guns inside the home.

"I'm not going to guess on what occurred in there, but obviously there were weapons in proximity to where kids are, and that's totally unacceptable to me," Dearborn Police Chief Ronald Haddad told reporters.

As many as 1.7 million American children live in homes with an unlocked, loaded gun, according to the Brady Campaign to Prevent Gun violence, and the incident was the latest case of children being injured by unsecured firearms.

Nearly 1,300 children die and 5,790 are treated for gunshot wounds each year in the United States, according to a recent study published in the medical journal Pediatrics.

Michigan state law does not prohibit guns at childcare facilities, television station WXYZ reported, but requires them to be unloaded and stored in a locked location away from children.

The home daycare was run by Samantha Eubanks, herself a mother of six who regularly took care of other children, according to neighbours and family members.

Ms Eubanks did not permit her husband Tim to keep weapons in their home, according to a woman identified by US media as her sister.

"She would always say don't you ever bring a gun in this house, it's not going to happen," Ashley Escobedo told assembled reporters at the scene.

The police chief told US media that the investigation was ongoing and charges were possible.