West of the city, authorities sealed off a section of a frozen lake where it was believed a sizable meteorite crashed through the ice.

But a team of divers has found no trace of any meteorite in the lake, an emergencies ministry spokeswoman told state media on Saturday.

The meteor was a once-in-a-century event, NASA officials said, describing it as a "tiny asteroid."

The space agency revised its estimate of the meteor's size upward late Friday from 49 feet (15 meters) to 55 feet (17 meters), and its estimated mass from 7,000 tons to 10,000 tons.

The space agency also increased the estimated amount of energy released in the meteor's explosion from about 300 to nearly 500 kilotons. By comparison, the nuclear bomb the United States dropped on Hiroshima in 1945 released an estimated 15 kilotons of energy.

The whole event, from the meteor's atmospheric entry to its disintegration in the air above central Russia, took 32.5 seconds, NASA said.

The national space agency, Roscosmos, said scientists believe one meteoroid entered the atmosphere, where it burned and disintegrated into fragments.

Amateur video footage showed a bright white streak moving rapidly across the sky before exploding with an even brighter flash and a deafening bang.

The explosion occurred about 9:20 a.m. local time, as many people were out and about.

A once in a lifetime event

Russians captured vivid images, many using dash cameras inside their vehicles.

Dash cameras are popular in Russia for several reasons, including possible disputes over traffic accidents and the corrupt reputations of police in many areas. Drivers install the cameras for their own protection and to document incidents they could be caught in.

Five regions of Russia, one of them Chelyabinsk, are thought to have been affected, Itar-Tass said. RIA Novosti cited emergencies ministry officials as saying three regions and Kazakhstan were involved.

NASA said on its website that the meteor was the largest reported since 1908, when the famous Tunguska event took place in remote Siberia.

In that incident, an asteroid entered the atmosphere and exploded, leveling about 80 million trees over an area of 820 square miles -- about two-thirds the size of Rhode Island -- but leaving no crater.

"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 at the Jet Propulsion Laboratory 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."

In what astronomers said was an unrelated coincidence, a larger asteroid, called 2012 DA14, passed relatively close to Earth around 2:24 p.m. ET Friday.

Stargazers in Australia, Asia and Eastern Europe could see the asteroid with the aid of a telescope or binoculars, but it never got closer than 17,100 miles to the planet's surface.

The Russian meteor was about one-third the size of the asteroid. The two bodies were on very different trajectories, scientists said.