TOWN OF MAPLE GROVE, Wis. (AP) — Four people remain hospitalized in Wisconsin burn centers with injuries from a bonfire explosion last week during a party in the Town of Maple Grove, authorities said Thursday.

The Shawano County Sheriff’s Office said the explosion happened late Friday when a 55-gallon drum that was a quarter-full of a mixture of gas and diesel fuel was placed on the fire.

The sheriff’s office said some of the victims are listed in critical condition but wasn’t specific.

Investigators say 17 of the injured people were privately transported to hospitals in Green Bay, which is about 25 miles north of the site of the explosion.

The sheriff’s office said it will not pursue any underage drinking violations in order to get witnesses to come forward. Authorities have said as many as 40 current and former Pulaski High School students were at the bonfire.