Intelligence sources in Washington were reported to be alarmed when they saw the giant fireball on satellite pictures. In Tokyo, the dollar began rising, as it usually does when disaster looms.
But it turned out that the blast was caused by a leak in a gas pipeline running through the remote tundra of the Komi autonomous region. Nobody was hurt, although forest was burnt.
The accident, on the ninth anniversary of the disaster at the Chernobyl nuclear power station, illustrated again the catastrophic state of much of the former Soviet Union's industrial infrastructure.
News of the explosion first came from the crew of a Japan Airlines jumbo jet passing over on a flight from Frankfurt to Tokyo. The pilot, Akira Nakagawa, said flames shot up to 20,000 feet. But Tass news agency, joining official attempts to play down the accident, said the fire rose no higher than 300 feet.
The pilot told a Narita airport news conference that clouds ahead of his plane had been turned bright red by the blaze and there was a black column of cloud. One passenger said the fire was "brighter than anything I've ever seen. It was as if the sun was climbing upward."
An official from the Ministry of Emergency Situations said: "There was a leak of gas and a spark probably set off the fire. Everything is OK now. There is nothing to worry about."
The blaze was so intense that firefighters could not immediately approach. Later they managed to bring it under control, Tass said. No deaths or injuries were reported.
This soothing tone will do little to appease Russia's increasingly active environmentalists, who say human life and nature are at constant risk from outdated and poorly maintained industrial plants. The energy network is in a particularly shabby state.
Yesterday's blast happened only 200 miles south of Usinsk, where late last year about 120,000 tons of oil spilled into the tundra. A hasty clean- up operation followed, but Russian ecologists fear rivers could be polluted when the snow starts to melt in coming weeks.
However, customers who buy Russian energy need not panic as a result of yesterday's blast. Gas officials were quick to point out that they had reserves and alternative pipeline routes to ensure exports did not suffer.