Three men died while attending a country music festival in Brooklyn, Michigan, and two more were critically injured, in what is believed to be a carbon monoxide leak, officials say.
Five people were found unresponsive on Saturday afternoon inside a travel trailer at a campground near the Faster Horses Festival, according to a statement from the Lenawee County Sheriff's Department.
Deputies from the sheriff's department found the five men and immediately began to administer CPR treatment to the victims, the statement said.
Three of the men died on site. Two of the men remain in critical condition and are being treated for acute carbon monoxide poisoning, according to the sheriff's office.
Authorities were responding to a 911 call from a friend of the five men who became concerned when he had not heard from them, the statement said.
Officials are investigating the deaths and injuries as the result of a suspected carbon monoxide leak from a generator located near the trailer.
The Faster Horses Festival describes itself as "Michigan's biggest 3-day country music & camping festival" and had begun on Friday in Brooklyn, about 40 miles west of Ann Arbor. Performers this year include Jason Aldean and Luke Combs.
The Faster Horses Festival did not immediately respond to a request for comment made by NBC News about the deaths.
A 30-year-old woman also died at the festival, but her death is unrelated to the suspected carbon monoxide poisoning. Police are investigating that death, too.
Officials urge those on the campgrounds to remember to keep exhaust fumes away from camping areas, tents and vehicles.