TOWN OF MUKWONAGO, Wis. (AP) -- A 17-year-old Wisconsin girl is in a coma after she was thrown from a speeding snowmobile and struck her head.

Town of Mukwonago police say the teen from Vernon was riding on the back of a snowmobile just after midnight Wednesday morning. The driver was a 21-year-old man who was speeding across the ice of Lower Phantom Lake when he swerved to avoid a car on the lake.

The rider and passenger were thrown from the snowmobile. Neither was wearing a helmet.

Police say they've received conflicting accounts of whether the car was parked or moving.

The girl was in critical condition Wednesday night.

Police Chief Grant Turner says alcohol wasn't a factor. The driver hasn't been charged with a crime, but Turner says that could change if drug tests are positive.