ARDMORE, Okla. (AP) _ A cabin cruiser exploded about 30 feet from a lake shore, killing a 5-year- old boy and burning five other people, three critically, authorities said.

The 26-foot boat's motor stalled shortly after it was launched into Lake Murray Saturday afternoon. As the boaters tried to restart the motor, gas fumes ignited a fireball that quickly engulfed the boat.

''It was completely ablaze from bow to stern. Smoke was visible from quite a ways back,'' lake patrolman Michael Key said Sunday. ''From what we can tell, two people were blown overboard.''

Lifeguard Monte Holland, 19, dragged two women ashore.

''I rushed down there and saw one little girl burned, sitting on the dock. I looked out and saw a guy who was trying to stay up and keep another lady afloat. She wouldn't have stayed afloat if somebody hadn't helped her,'' Holland said. ''I went out and got her and then went back in and helped another lady. I did what I had to do.''

Bryan Jordon, 5, died of burns at the scene, according to the Oklahoma Lake Patrol.

Passengers Cheryle Jordan, 29 and Sarah Weatherford, 26, were in critical condition Sunday with burns, authorities said. A Children's Hospital of Oklahoma spokeswoman said Rachael Weatherford, 5, improved to serious condition late Sunday after being admitted in critical condition with second- and third-degree burns over 70 percent of her body.

Blane L. Fore, 30, the driver of the boat, was in fair condition Sunday with burns on his leg, and Kenneth Scott Jordan, 29, was in serious condition.

Lake Murray is about 30 miles north of the Texas-Oklahoma border and 140 miles south of Oklahoma City.