Thousands of Russian emergency workers have been deployed to clear up the damage from a meteor that exploded over the Ural mountains on Friday, damaging buildings, shattering windows and showering people with broken glass.

"It was eerie," Alyona V Borchininova, a barmaid, said yesterday recalling how she and several other residents of the Westren Siberian town of Chebarkul watched the streak of light that passed across the sky on Friday morning. "We stood there. And then somebody joked, 'Now the green men will crawl out and say hello'."

Yesterday divers searched a lake near the city of Chelyabinsk, where a hole several metres wide had opened in the ice, but had so far failed to find any large fragments of the meteor, officials said.

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The scarcity of evidence on the ground fuelled scores of conspiracy theories over what caused the fireball and its huge shockwave on Friday in the area which plays host to many defence industry plants.

Russian nationalist leader Vladimir Zhirinovsky told reporters in Moscow it could have been "war-mongers" in the United States. "It's not meteors falling. It's a new weapon being tested by the Americans," he said.

A priest from near the explosion site called it an act of God. Social media sites were flooded with speculation.

Oksana Trufanova, a local human rights activist, said: "Honestly, I would be more inclined to believe that this was some military thing."

Asked about the speculation, an official at the local branch of Russia's Emergencies Ministry simply replied: "Rubbish."

Residents of Chelyabinsk, an industrial city 950 miles east of Moscow, heard an explosion, saw a bright light and then felt a shockwave that blew out windows and damaged the wall and roof of a zinc plant.

The fireball – travelling at 19 miles per second, according to Russian space agency Roscosmos – blazed across the horizon, leaving a long white trail visible as far as 125 miles away.

US space agency Nasa estimated the object was 55 feet across before entering Earth's atmosphere and weighed about 10,000 tonnes. It exploded miles above Earth, releasing nearly 500 kilotons of energy – about 30 times the size of the nuclear bomb dropped on the Japanese city of Hiroshima in the second world war.

"We would expect an event of this magnitude to occur once every 100 years on average," said Paul Chodas of Nasa's Near-Earth Object Program Office in California. "When you have a fireball of this size, we would expect a large number of meteorites to reach the surface and in this case there were probably some large ones."

Search teams yesterday said they had found small objects up to about half an inch wide that might be fragments of a meteorite, but no larger pieces.

The Chelyabinsk regional governor said the strike caused about one billion roubles (£21 million) worth of damage.

Life in the city had largely returned to normal yesterday although 50 people were still in hospital. Officials said more than 1200 people had been injured, mostly by flying glass.

Repair work had to be done quickly because of the freezing temperatures, which sank close to -20C at night.

Emergencies minister Vladimir Puchkov inspected the damage after President Vladimir Putin sent him to the region.

His ministry is under pressure to clean up fast following criticism over the failure to issue warnings in time before fatal flooding in southern Russia last summer, and over its handling of forest fires in 2010.

Putin will also want to avoid a repeat of the criticism he faced over his slow reaction to incidents early in his first term as president, including the sinking of the Kursk submarine in 2000 which killed all 118 people on board.