LOS ANGELES, FEB. 1 -- A USAir Boeing 737 jetliner crashed onto a runway at Los Angeles International Airport tonight, hitting a twin-engine Sky West commuter flight and skidding into a building, apparently on top of the smaller twin-prop plane, killing at least five people and injuring at least 25.

The USAir plane was flying from Syracuse, N.Y., to San Francisco by way of Washington, Columbus, Ohio, and Los Angeles. USAir officials said 33 of the 83 passengers boarded the plane in Washington. The Sky West plane was scheduled to take off for Palmdale, Calif.

The Federal Aviation Administration (FAA) said there were 101 people on the two planes and that 29 of them were unaccounted for 2 1/2 hours after the accident, which occurred at 6:08 p.m. (9:08 p.m. EST). USAir officials said that 57 of the 72 people who had been accounted for were either uninjured or had minor injuries.

National Transportation Safety Board spokesman Jeff Rich said the death toll could rise beyond 15.

Los Angeles Mayor Tom Bradley, after conferring with fire officials, said, "The larger plane dragged the smaller plane for several hundred yards before they crashed into the building."

Deputy Fire Chief Davis R. Parsons said firefighters had decided to wait until daylight "before we go in an extricate the bodies from the aircraft." He said there was still fuel leaking from lines in both aircraft, making it too dangerous to approach until all fuel had been cleared away. He declined to comment on whether anyone remaining inside either aircraft might still be alive.

Bradley said the fire was so intense that it "destroyed the interiors of the planes completely."

The FAA regional spokeswoman in Los Angeles, Elly Brekke, told Cable News Network tonight that the two planes collided on the runway. "The USAir flight was landing . . . the Sky West was preparing to take off for Palmdale, Calif. We do not know the cause; we know it involved one airplane taking off and one landing."

Brekke said the planes collided on Runway 24L, one of two parallel runways on the airport's north side. She said the airport remained open, using two runways on the south side of the field.

Television broadcast reports, which provided scenes of ambulances and fire trucks circled around the USAir jetliner, did not show the Sky West plane.

USAir officials in Los Angeles said Flight 1493 was carrying 83 passengers and a crew of six. It was a Boeing 737-300, a late model of the popular twin-engine jetliner configured to carry 128 passengers.

The commuter plane was identified as Sky West Flight 5569, leaving Los Angeles for Palmdale. That flight is scheduled for a twin-engine Fairchild Metro, which can carry about 19 passengers. News reports from the scene said there were 10 passengers and two crew members aboard.

Alysse Rosewater, 22, of Cincinnati who was flying with her cousin, Laurel Bravo, 24, of Cleveland, told Reuter they felt lucky to be alive. "We knew that some people were either dead or injured because none of the passengers around us came out of the plane," Bravo said.

Rosewater said she felt one "hit," then a second. "I guess that was when we struck the building," she told Reuter. "At first I thought it was just a bumpy landing, then the cabin filled with smoke and there was fire on both sides.

"I was terrified. My cousin and I tried to head for the door and all of a sudden we were pushed through a window," Reuter reported her as saying. "I think it must have been an emergency exit, and we ended up on the wing."

Other passengers said the plane filled with smoke as they struggled to leave, helped by firefighters, from the front of the plane, Reuter reported.

There were conflicting eyewitness reports from the scene, a normal occurrence in airliner crashes. Some on the scene said the 737 came in with its landing gear up, but a USAir spokesman in Washington said he had been assured by USAir operations officials that was not true. There was also the possibility that the smaller plane had pulled onto the runway.

"The {USAir} pilot did not report any type of emergency to the control tower when the plane was landing," FAA spokeswoman Brekke told CNN. "There was no emergency declared."

USAir passenger Gary Dunham, of Moorpark, said, "We had a good landing. We were braking the engine." Then there was a thud and a flash of fire. He said he got out because he was close to one of the exits.

With the Persian Gulf War underway, there was also the question of whether terrorism could have been involved. However, David Shipley, a spokesman for USAir in Washington said there was no indication terrorism was involved "at this time."

Airport officials initially indicated the Boeing 737 had hit a utility building near the runway. USAir spokeswoman Agnes J. Huff said the building was an unused former firehouse. The rear of the jetliner was engulfed in blinding flame and smoke shortly after the crash and appeared to have snapped in two. Firefighters using foam appeared to put the fire out after about 40 minutes.

USAir employees inside Terminal 1, the airline's main terminal here, escorted about 25 pasengers, apparently unhurt but wrapped in blankets, away from the crash site and into a room at the airport.

Parsons said 12 injured people, seven in critical condition, were taken to five local hospitals shortly after the crash. Later, another 14, all of whom had relatively minor injuries, were hospitalized, including one firefighter.

Several passengers were treated at the scene for smoke inhalation and minor injuries. One of the city's leading burn centers, Sherman Oaks, reported receiving only one patient from the collision.

Rudolph Morfin, 48, of Downey, had boarded Flight 1493 in Washington and was one of two people taken from the crash to Robert F. Kennedy Medical Center in Hawthorne for treatment of second-degree burns to his arms, back and face before being transferred to another hospital. A source at the hospital said Morfin said he had jumped 10 feet from the jetliner to the ground after having helped a young woman out of the plane.

"That sounds like him," said Morfin's brother, Charlie, when he heard that he had helped another passenger. He said he and his brother had been involved in rescues when they were on horseback trips.

Morfin's wife, Dolores, said her husband said he heard a "thud" before the seat behind him crashed into his and the plane almost immediately filled with smoke. She said he bumped his head when he jumped from the plane and ended up under the wing.

Flight 1493 is equipped to carry as many as 128 passengers, Huff said. She said people waiting for the arrival of the flight had been escorted to a private room in the airport to await further information and possible reunion with survivors. Airport security blocked reporters from entering the waiting section of Terminal 1 for USAir flights.

Tonight's runway collision was the second in two months. On Dec. 4, two Northwest Airlines jetliners collided on a fog-covered runway at Detroit Metropolitan Airport, killing eight people and injuring more than 20.

In that accident, a Northwest Boeing 727 was racing toward takeoff when it slashed into a taxiing DC-9, which had turned in front of it. An ensuing fire moved quickly through the DC-9, which had 39 passengers and four crew members aboard. The 145 passengers and eight crew members on the 727 were uninjured.

The last major accident in the Los Angeles area involved a midair collision in August 1986 that killed 82 people. In that crash, an Aeromexico DC-9 hit a small plane over the suburb of Cerritos.

Staff writer Don Phillips in Washington and staff writer Lou Cannon and special correspondent Jill Walker in California contributed to this report.