CLINTON, Wis. -- The Rock County Sheriff's Office said it is investigating a fatal one-vehicle crash and a separate three-vehicle crash that both occurred Wednesday afternoon on Highway 14.

At 1:50 p.m. Wednesday, members of the Rock County Sheriff's Office and Clinton Fire/EMS responded to a one-vehicle crash at the intersection of U.S. Highway 14 and Kemp Road.

Authorities said an investigation indicates that a westbound vehicle on Highway 14 left the roadway, hit a tree, rolled and burst into flames. The driver was killed on impact, authorities said. Investigators said they don't believe that speed was a factor in the crash.

At about 2:30 p.m., Highway 14 had been reopened to traffic and the roadway was clear.

Authorities said they were still at the scene of the fatal crash when an eastbound pickup truck driven by a driver from Footville stopped in the traffic lane on Highway 14. This pickup truck was hit from behind by a Williams Bay school bus, authorities said.

The pickup truck then spun into the westbound lane of traffic hitting a westbound car driven by a Janesville man, authorities said.

At the time of the crash there were five children on the bus. Authorities said the children were checked by EMS personnel and released at the scene.

Sheriff's officials said the pickup truck driver and his passenger were transported to Mercy Hospital and their condition is unknown.

The driver of the car was uninjured. A child in a child safety seat in the car was transported to Mercy Hospital and the child's condition is unknown, authorities said.

Rock County Sheriff's Office is being assisted by the Wisconsin State Patrol and the Rock County Humane Society, which removed an injured dog from the truck.

Authorities said Highway 14 is closed and is not expected to reopen until about 5 p.m. Wednesday.

The Rock County Sheriff's Office said it is continuing to investigate.