Scores of Russian children heading for the holiday of their lives died when their plane collided with a cargo jet over Germany, leaving the resort of Lake Constance strewn with bodies and burning debris.

Officials said 71 people, including 52 children and teenagers, were killed in the Monday night crash between a Bashkirian Airlines jet bound for Barcelona, Spain, and a Boeing 757 cargo jet operated by the international courier company DHL.

The children had only been on the plane, chartered at the last minute, because they had missed an earlier flight. "If they had flown on time, none of this would have happened," the distraught mother of 14-year-old victim Bulat Biglov said.

The collision prompted experts to question the safety commitment of Russian airlines, as Russian and Swiss air officials began to trade blame for the disaster.

Witnesses said they heard rolling thunder and saw an orange glow and fireballs resembling comets in the night sky.

A black rain of wreckage then poured down on the northern shore of this picturesque lake in southwestern Germany. Eyewitnesses described how the collision turned this region of chocolate-box beauty into a scene from hell in seconds.

"We came across five bodies just lying in the field next to each other," said Wolfgang Steiner, gardener at a children's home just 200 metres from where the tail section of the Tupolev 154 airliner came crashing down.

"One had his neck broken, one was missing a foot but there was no blood. I kept saying to myself, why is there no blood? They were adults, but they looked so small lying in that field."

There were 69 Russians on board the seven-year-old Tupolev and a crew of two, a Briton and a Canadian, on the Boeing 757 bound for Brussels.

Swiss air traffic controllers, in charge of Lake Constance airspace because it is close to Switzerland, said the Tupolev reacted too slowly to orders to lower its altitude.

They said the Russian pilot got Swiss orders to decrease altitude a "good minute" before the collision but German media reported the warning was given 50 seconds before the crash.

"The way our colleague worked was cutting it close, but absolutely acceptable," Anton Maag - an official at Skyguide, the Swiss air traffic controllers body monitoring the flights on Monday night - told a news conference yesterday.

Swiss air traffic controllers said earlier it was only on the third instruction that the Russian pilot had begun to reduce altitude to avoid collision.

By the time the Tu-154 began to descend, the 757 was also diving because its on-board collision-avoidance system had instructed its pilot to do so. So the planes hit each other in one of the worst air accidents in German history.

Maag said the air traffic controller in charge at the time was working alone as his partner took a break because of the light air traffic. Five planes were in the sector they were monitoring at the time, which included the two crashed planes.

Bashkirian Airlines denied the Tupolev crew had made any mistakes. "My version is that the (air) traffic controllers are to blame," Nikolai Odegov, the airline's director, said in Moscow.

Aviation safety analyst Chris Yates said Russian airlines had a poor crash record, which he said generally stemmed from failure to follow correct procedures, not from faulty planes.

The Tupolev should also have been fitted with a collision warning system, which all planes flying over Europe are obliged to use, airline experts said.

"This was the accident that could not happen," David Learmont, another air safety expert, said.

Russian Prime Minister Mikhail Kasyanov described the collision as a "terrible tragedy" and said the cause was a mystery. "The scope of this tragedy is beyond understanding," he said after meeting French President Jacques Chirac in Paris.

Chancellor Gerhard Schroeder sent his "heartfelt condolences" to Russian President Vladimir Putin, and Pope John Paul said the victims would be in his prayers.

Germany said it would issue special visas to relatives seeking to visit the crash site. Russian crash investigators were expected to arrive late yesterday.

Families along the shore of Lake Constance were counting their blessings at special church services late yesterday as they recalled how tonnes of flaming aircraft wreckage crashing out of the sky missed their homes by a whisker.

There were no casualties on the ground even though police said they found pieces of wreckage in at least 57 different places.

"In the glow of the fire I saw wreckage falling out of the sky. It looked like black rain," said Klaus-Dieter Schindler, a janitor at a school in the village of Owingen.

Debris was scattered over an area of more than five square kilometres around Ueberlingen, a resort town of 20,000.

The Russian youths, mostly children from the political elite in Russia's oil-rich, mainly Muslim, region of Bashkortostan, were heading for a Unesco festival in Barcelona.

Airline officials said many of the passengers on the flight had the same surname, indicating families may have lost more than one relative.

The young passengers were looking forward to two weeks of fun and sun at a four-star Spanish hotel by the Mediterranean.

Everything was ready at the Estival Park Hotel in the seaside resort of Salou. The tragedy stunned staff at the hotel in the modern Costa Dorada beach resort near Barcelona.

"We were expecting 43 children between eight and 16. Everything was ready and the coach driver was waiting at the airport. It's a terrible tragedy," said a spokesman for the hotel, just 200 metres from the beach.

Rescue workers had recovered about 26 bodies and a large number of body parts by mid-afternoon yesterday as well as the Tupolev flight data recorder, vital for crash investigation.

Helicopters with infrared cameras clattered overhead as more than 800 rescue workers combed the area.

The airline, based in Bashkortostan, was one of many to emerge from the break-up of the state airliner Aeroflot after the collapse of the Soviet Union. It relies mainly on a fleet of Tu-154s, Russian planes commonly used for medium-range flights.

The two planes were flying at an altitude of 35,300 feet above Ueberlingen at the northwest end of Lake Constance when they collided, Swiss air traffic controllers said.

A spokesman for German flight control said there had been no problems contacting the Tupolev while it was in German airspace. A DHL spokesman said there were no problems with their plane before the crash.

The cargo flight, operated by DHL Worldwide Express, which is majority-owned by Deutsche Post, originated in Bahrain and had taken off from Bergamo in Italy en route to Brussels.

Tu-154s have crashed several times over the past year. An Iran Air Tours Tu-154 crashed in February in Iran killing all 119 aboard. A year ago 136 passengers and nine crew were killed when a Russian Tu-154 crashed in Siberia.