A shooter has opened fire at a water park in the US state of Michigan, wounding nine or more people including at least one child, police said on Sunday.

The local sheriff's office said it potentially had the suspect contained near the scene of the shooting in Rochester Hills, a suburb of Detroit.

"It appears like the individual pulled up, exited a vehicle, approached the splash pad, opened fire. Reloaded, opened fire. Reloaded. Left. So it appears very random at this point," Sheriff Michael Bouchard of Oakland County told reporters, adding he believed the shooter had "no connectivity to the victims."

He said preliminary information indicated there were nine to 10 victims of varying ages, including one eight-year-old child. Several hospitals have received patients, he said.

A Glock handgun and empty magazines were recovered at the scene.

According to Bouchard, "we believe we have an individual who's a suspect contained nearby."

He said that assets including SWAT teams and armoured vehicles have been deployed.

Michigan Governor Gretchen Whitmer said she was "heartbroken" to learn of the shooting.

"We are monitoring the situation as updates continue to come in, and are in touch with local officials," she said on social media platform X.

Gun violence in the United States is common, and thousands of Americans are killed each year in shootings. Efforts at broad reforms to the nation's gun laws have been stymied for decades. (AFP)