HAZELHURST, Wis. (AP) — Three people are dead after a medical helicopter crashed in a heavily wooded area in northern Wisconsin, authorities said Friday.

The helicopter went missing late Thursday night. Search rescue crews reached the crash site early Friday, according to the Oneida County Sheriff's Office.

Chief Deputy Dan Hess said the crash involved an Ascension Wisconsin Spirit helicopter, but he said he doesn't know if the three victims were all Ascension employees. The sheriff's office referred other questions from The Associated Press to Ascension Health, which didn't immediately respond to calls and emails Friday morning.

The sheriff's office said the helicopter was later located in Hazelhurst, a small town about 150 miles (241 kilometers) northwest of Green Bay.

Authorities say the last known contact with the helicopter was at 10:55 p.m. Thursday. Dispatchers received a call that the chopper was missing 25 minutes later, and a search was later launched.

A witness who drove search crews to the scene on an amphibious all-terrain vehicle says the chopper went down in a heavily wooded area with high ridges and some swamps.

At least eight agencies were involved in the search.