At least 11 people have been injured in a stabbing at a Walmart supermarket in Michigan, authorities say.

A 42-year-old suspect was in custody following the incident in Traverse City, authorities confirmed.

A nearby hospital said it was treating 11 victims. “As a result, our Emergency Department is currently experiencing a higher-than-usual volume of patients,” Munson Medical Centre said on social media.

Footage posted online shows multiple police and ambulance units in the carpark of the Walmart.

Grand Traverse County Sheriff’s Office confirmed it was investigating “a multiple stabbing incident at the Wal-Mart in Traverse City”.

The suspect is a Michigan resident and used a “folding knife style weapon”, Sheriff Michael Shea told reporters. The incident appeared to be a “random act”, he added.

He said people in the store assisted in apprehending the man and helped treat the injured.

“This was a joint effort all the way through, and, as I mentioned, the citizens, too,” Shea said of the response.

As of Saturday night, five people were in a serious condition, while six others were critical.

FBI Deputy Director Dan Bongino said federal personnel were responding to provide any necessary support to local authorities.

Michigan Governor Gretchen Whitmer said she was “in touch with law enforcement about the horrible news”.

“Our thoughts are with the victims and the community reeling from this brutal act of violence,” she added.

Traverse City is about 255 miles (410 kilometres) northwest of Detroit.