WARREN, Maine (AP) _ A tour bus collided head-on with a car Saturday, killing four people and injuring 20, authorities said.

The accident occurred shortly before 4 p.m. on U.S. 1 and involved a Travel Tours of Oklahoma bus carrying 43 people, many of them senior citizens, state police Sgt. Herbert Cram said.

The dead, including an 8-year-old boy and a pregnant girl, were in the car, officials said.

A 10-year-old boy was hospitalized in fair condition, said Penobscot Bay Medical Center spokesman Russell Donahue. The remaining injured were treated and released.

The car, traveling south, hit the bus and a second car, unable to avoid the wreckage, slammed into the car, witnesses said.

The first car ''veered off and hit the bus head-on, and that threw him right into me,'' said Edwin Antz, the driver of the second car.

The first car burst into flames. People from a nearby campground pulled a boy from the car, then put the fire out.

The bus passengers were from Oklahoma and Arkansas, and were on their way to Bangor, said Travel Tours guide Emmy Stidham.

Police identified the dead as Kenneth Prior, 18, of Waldoboro, the driver; his fiancee, Marilyn McDougal, 17, of Warren, who was seven months pregnant; her 8-year-old brother, Adam, and Donald Grant, 18, of Thomaston.