MORGANTON, N.C. (AP) _ Firefighters hosed down the smoking ruins of a school today to allow investigators to enter in a search for the cause of a fiery explosion that ripped through the building as a basketball game went on next door.

No injuries were reported Tuesday in the blast at the Salem Junior High School that rocked houses for several blocks, threw the school's locked doors 60 to 70 feet and blew out windows and doors in a nearby elementary school.

Flames could be seen 10 miles away, witnesses said.

''I thought someone had hit the house with a car,'' said W.G. Biggerstaff, who lives about a quarter-mile away.

The U.S. Bureau of Alcohol, Tobacco and Firearms was called in to investigate by state and local officials because of the magnitude of the explosion, said Ray Robinson of Burke County Emergency Management Services.

''This explosion is not consistent with anything that should have been in that building,'' said EMS Director Nick Waters.

''It was not consistent with an explosive device like dynamite,'' he said. ''It was consistent with the type of explosion caused by natural gas.''

Waters said the building is heated by an oil furnace and propane was used in the kitchen in the building's basement.

He said heavy equipment would be needed to shore up the structure so officials could investigate.

The explosion rocked the school at 7:30 p.m. while a game between teachers and Little League coaches was under way in an adjacent gymnasium.

The school's walls were left standing, but the interior was destroyed. About 70 firefighters brought the blaze under control about three hours after the explosion.

The blast and fire damaged several cars parked in front of the school and shattered windows in the gym, witnesses said. The explosion was heard up to four miles away, Robinson said.

''We were just about at the entrance to the school when it went off,'' said Dennis Leonard, who was driving to the game after it had begun. ''We saw the fire come out the right front side of the building and heard a big explosion.

''We drove up there from stupidity, I guess,'' he said. ''It was obvious that the windows were all blown out and people started coming out of the gymnasium.

''For no one to be hurt, it is very fortunate,'' he said. ''As sad as this is, it could have been a lot worse.''

Jim Wilson, county superintendent schools, said classes were canceled today at the elementary and junior high schools. He said he would look to the community for help in scheduling classes.

''My plans are to begin asking churches and people in the community to donate space wherever we can have classes,'' he said.

Allen Causby, who was at the basketball game, said he ran outside and saw his car covered in glass.

''I looked up at the building and it was just all gone, totally gone. I had just gotten there 15 minutes earlier and had noticed nothing unusual,'' he said.

''It was a great big boom and it rocked the house,'' said Faye Ross, who lives across the street from the school.