Two Boeing 747 airliners collided on a foggy runway on this Canary Island today and burst into flames killing hundreds of vacationers.

There were widely differing reports of the death toll. The Dutch airline KLM said all 249 persons aboard its plane were killed. There was no firm figure of the number who died in the other plane, Pan American World Airways charter flight from Los Angeles. Pan Am said the plane had 394 persons aboard.

The Spanish news agency Cifra reported that 570 persons were killed, and at least 67 were injured. If this figure is accurate, today's crash would be the worst in aviation history. The highest previous death toll was the 346 persons killed when a Turkish DC-10 crashed outside Paris on March 3, 1974.

Both planes were carrying tourists on charter trips and both had been diverted from intended landings at Las Palmas on a sister island because of a bomb blast there. The Canary Islands are off the coast of Morocco in the Atlantic Ocean.

Pan Am said both planes had spent time on the ground at Santa Cruz, on the island Tenerife, and were preparing to take off again when the collision occurred. It said its plane was crossing a runway when the collision took place.

A spokesman for Pan Am in New York said the copilot of its plane, R. L. Bragg, had called from a hospital in Santa Cruz and said: "Visiblity was poor and suddenly there was another aircraft and a collision." Bragg said the pilot of the plane, V.F. Grubbs, also survived. The copilot was believed to have a broken leg.

Cifra said a time bomb had exploded at the Las Palmas airport some three hours before the Santa Cruz accident. Eight persons were injured, it said, when a bomb hidden in a vase blew up in a flower shop.

No organization has claimed responsiblity for the bombing, the agency said, but a separatist movement has been blamed for previous bombing incidents on the islands, which are Spanish.

Airport sources here said the volume of air traffic over Tenerife had reached the saturation point as a result of the closure of the airport on Las Palmas.

"You couldn't see the runway from the airport building, the fog was that thick," said Eduardo Urbano, a Santa Cruz resident who arrived at the airport within an hour after the collision.

Urbano said parts of both planes and bodies were scattered over the runway and "a wing broke off from one plane that was in flames."

["There are definitely some survivors," a Pan American official in London reported. "As to how many there are, we don't know yet."]

In a telephone interview, the administrator of the Santa Cruz General Clinic said 13 Americans were admitted there and two were in critical condition. Seventeen other Americans were admitted to a second local hospital and they were all in fair-to-good condition, a doctor reported.

Cifra said the Santa Cruz airport, Rodeos, was in heavy fog at the time of the accident and that one of the planes preparing to depart crossed into the second jet's takeoff path.

An airport spokesman said the Pan Am 747 was taxiing towards its takeoff point when it crossed a runway and was hit by the KLM 747, he said.

The airport was immediately closed to all flights after the crash at 4:40 p.m. (11:40 a.m. EST). All radio and television stations on Tenerife broadcast appeals to doctors and other medical personnel to report to their hospitals because of the "utmost emergency."

The Americans aboard the Pan American flight life Los Angeles yesterday, and were on their way to a cruise to a number of Mediterranean ports aboard the M.S. Golden Odyssey, which awaited their arrival in Las Palmas. A spokesman for Royal Cruise Line said the passengers came from all over the western United States.

Jim Novik, a travel agent from San Francisco, who was aboard the Pan American jet, said: "From where I was sitting in the first-class compartment, I heard an explosion. Then the ceiling caved in.

"A piece of the ceiling fell on my wife as I was trying to unfasten her seat belt there was another explosion, which threw her out of the plane."

Novik added: "I jumped out of the plane just before it was engulfed by flames."

Most of the survivors of the crash suffered burns and fractures, doctors said.

Cars choked the road to the airport tonight as people drove out to watch the blazing planes. Flames lit the middle of the runway and a thick pall of smoke hung over the airport.

(The National Transportation Safety Board dispatched a team of experts from Washington to the Canary Islands to offer to assist Spanish authorities in investigating the crash. The U.S. Embassy in Madrid also sent a team to the scene.)

The only previous crash of a Boeing 747 passenger jet occurred Nov. 20, 1974, in Nairobi, Kenya. The Lufthansa plane crashed on takeoff, killing 59 of the 157 persons aboard. A 747 outfitted for cargo hauling by the Iranian air force crashed on landing last year at the Madrid airport.

Santa Cruz airport has been the scene of several air accidents. The last major crash occurred on Dec. 3, 1972, when a Spanish Convair 990 jet carrying German tourists was caught by a sudden cross winds on takeoff, flipped over and crashed, killing all 155 persons aboard.