With a blinding flash and a booming shock wave, a meteor blazed across the western Siberian sky Friday and exploded with the force of 20 atomic bombs, injuring more than 1,000 people as it blasted out windows and spread panic in a city of 1 million.

While NASA estimated the meteor was only about the size of a bus and weighed an estimated 7,000 tons, the fireball it produced was dramatic. Video shot by startled residents of the city of Chelyabinsk showed its streaming contrails as it arced toward the horizon just after sunrise, looking like something from a world-ending science-fiction movie.

The largest recorded meteor strike in more than a century occurred hours before a 45-metre asteroid passed within about 28,000 kilometers of Earth. The European Space Agency said its experts had determined there was no connection between the asteroid and the Russian meteor — just cosmic coincidence.

The meteor above western Siberia entered the Earth's atmosphere about 9:20 a.m. local time at a hypersonic speed of at least 54,000 km/h and shattered into pieces about 30-50 kilometers high, the Russian Academy of Sciences said. NASA estimated its speed at about 65,000 km/h, said it exploded about 19 to 24 miles high, released 300 to 500 kilotons of energy and left a trail 485 kilometres long.

"There was panic. People had no idea what was happening," said Sergey Hametov of Chelyabinsk, about 1,500 kilometers east of Moscow in the Ural Mountains.

"We saw a big burst of light, then went outside to see what it was and we heard a really loud, thundering sound," he told The Associated Press by telephone. Saskatoon native Michael Garnett, a goaltender for Traktor Chelyabinsk in the Kontinental Hockey League, told CBC News he was terrified by the noise, which was so loud he was convinced something had happened right next to his building.

"I thought for sure there was an explosion, and then I thought it might have been a natural gas leak or it could have been a bomb or a missile or a plane crash," he said. The shock wave blew in an estimated 100,000 square metres of glass, according to city officials, who said 3,000 buildings in Chelyabinsk were damaged. At a zinc factory, part of the roof collapsed.

The Interior Ministry said about 1,100 people sought medical care after the shock wave and 48 were hospitalized. Most of the injuries were caused by flying glass, officials said. Another Chelyabinsk resident, Alexander Yakovets, told CBC News he was woken in his eighth-floor apartment by a "really horrible sound" that he first thought might have been a terrorist attack or a military exercise. He said he saw a very bright light and heard multiple explosions.

Shattered windows

"For a couple of minutes, I thought [the building] was going to fall down," he said. Scientists estimated the meteor unleashed a force 20 times more powerful than the Hiroshima bomb, although the space rock exploded at a much higher altitude. Amy Mainzer, a scientist at NASA's Jet Propulsion Laboratory, said the atmosphere acted as a shield.

The shock wave may have shattered windows, but "the atmosphere absorbed the vast majority of that energy," she said.

Emergency Situations Ministry spokesman Vladimir Purgin said many of the injured were cut as they flocked to windows to see what caused the intense flash of light, which momentarily was brighter than the sun.

There was no immediate word on any deaths or anyone struck by space fragments.

The meteor's shockwave damaged around 3,000 buildings including this zinc factory, where about 600 square metres of the roof collapsed. (Oleg Kargapolov/Chlyabinsk.ru/AP)

President Vladimir Putin summoned the nation's emergencies minister and ordered immediate repairs. "We need to think how to help the people and do it immediately," he said.

Some meteorite fragments fell in a reservoir outside the town of Chebarkul, the regional Interior Ministry office said. The crash left an eight-metre crater in the ice.

Lessons had just started at Chelyabinsk schools when the meteor exploded, and officials said 258 children were among those injured. Amateur video showed a teacher speaking to her class as a powerful shock wave hit the room.

Yekaterina Melikhova, a high school student whose nose was bloody and whose upper lip was covered with a bandage, said she was in her geography class when a bright light flashed outside.

"After the flash, nothing happened for about three minutes. Then we rushed outdoors. ... The door was made of glass, a shock wave made it hit us," she said.

Largest since 1908

Meteors typically cause sizeable sonic booms when they enter the atmosphere because they are traveling so much faster than the speed of sound. Injuries on the scale reported Friday, however, are extraordinarily rare.

The many broken windows exposed residents to the bitter cold as temperatures in the city were expected to plummet to minus 20 Celsius overnight. The regional governor put out a call for any workers who knew how to repair windows.

A circular hole in the ice of Chebarkul Lake where a meteor reportedly struck near Chelyabinsk. (Associated Press)

Meteoroids are small pieces of space debris — usually parts of comets or asteroids — that are on a collision course with the Earth. They become meteors when they enter the Earth's atmosphere. Most meteors burn up in the atmosphere, but if they survive the frictional heating and strike the surface of the Earth they are called meteorites.

NASA said the Russian fireball was the largest reported since 1908, when a meteor hit Tunguska, Siberia, and flattened an estimated 80 million trees. Chelyabinsk is about 5,000 kilometers west of Tunguska. The Tunguska blast, attributed to a comet or asteroid fragment, is generally estimated to have been about 10 megatons.

Scientists believe that a far larger meteorite strike on what today is Mexico's Yucatan Peninsula may have been responsible for the extinction of the dinosaurs about 66 million years ago. According to that theory, the impact would have thrown up vast amounts of dust that blanketed the sky for decades and altered the climate on Earth.

'Difficult to detect'

The object hailed from the asteroid belt between Mars and Jupiter, becoming a meteor as it streaked through the earth's atmosphere, Bill Cooke, head of the Meteoroid Environments Office at NASA's Marshall Space Flight Center in Huntsville, Alabama, said.

Meteor, meteoroid, or meteorite? Small pieces of space debris — usually parts of comets or asteroids — that are on a collision course with the Earth are called meteoroids. When meteoroids enter the Earth's atmosphere and burn up in a flash of light, they are called meteors (or "shooting stars"). If they survive the frictional heating and strike the surface of the Earth, they are called meteorites.

Paul Chodas, research scientist at the Near-Earth Object Program Office at the Jet Propulsion Laboratory, said that ground telescopes would have needed to point in the right direction at the right time to spot Friday's incoming meteor.

"It would be very faint and difficult to detect, not impossible, but difficult," Chodas said.

Experts said the Russian meteor could have produced much more serious problems in the area hosting nuclear and chemical weapons disposal facilities.

Vladimir Chuprov of Greenpeace Russia noted that the meteor struck only 100 kilometres from the Mayak nuclear storage and disposal facility, which holds dozens of tons of weapons-grade plutonium.

The panic and confusion that followed the meteor quickly gave way to typical Russian black humour and entrepreneurial instincts. Several people smashed in the windows of their houses in the hopes of receiving compensation, the RIA Novosti news agency reported.

Others quickly took to the Internet and put what they said were meteorite fragments up for sale.

One of the most popular jokes was that the meteorite was supposed to fall on Dec. 21, 2012 — when many believed the Mayan calendar predicted the end of the world — but was delivered late by Russia's notoriously inefficient postal service.