A meteor streaked through the skies above Russia's Urals region Friday morning, before exploding with a flash and boom that shattered glass in buildings and left hundreds of people hurt.
The number of injured continues to rise as new reports come in from across a wide area.
As of noon Moscow time, as many as 725 people had sought medical help, according to the state-run RIA Novosti news agency.
Deputy Health Minister Igor Kagramanyan said 571 people had sought medical help, with 34 of them hospitalized, according to state-news agency Itar-Tass.The vast majority of injuries are not thought to be serious.
About 270 buildings have sustained damage -- mostly broken glass -- as a result of the shock waves caused by the blast, said Vladimir Stepanov, of the National Center for Emergency Situations at the Russian Interior Ministry.
Hospitals, kindergartens and schools are among those affected, he said.
About 20,000 emergency response workers have been mobilized, RIA Novosti reported.
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.
The national space agency, Roscosmos, said scientists believed one meteoroid had entered the atmosphere, where it burned and disintegrated into fragments, according to RIA Novosti.
The resulting meteorites are believed to be scattered across three regions of Russia, one of them Chelyabinsk, as well as neighboring Kazakhstan, the news agency said.
One large chunk was discovered in a lake in the Chelyabinsk region, RIA Novosti cited the Chelyabinsk governor as saying.
A spokesman for the Emergency Ministry for the Chelyabinsk region told CNN that the latest information it had was that 524 people there were injured and 34 hospitalized.
NASA estimates 4,700 'potentially hazardous' asteroids
For sky watchers, the reports bring to mind the famous Tunguska event of 1908 in remote Siberia, in which an asteroid entered the atmosphere and exploded, leveling trees over an area of 820 square miles -- about two-thirds the size of Rhode Island.
About 80 million trees were felled, radiating out from the center of the blast, but no crater was left.Friday's Chelyabinsk meteor comes on the same day that a hefty asteroid is due to charge past Earth at a pretty close range, in space terms.
An asteroid is coming. Fear not, scientists say
Known as 2012 DA14, the asteroid is thought to be 45 meters long, about half the length of a football field.
But scientists say it will come no closer than 17,100 miles from our planet's surface.
Your photos: Orionid meteor shower
"No Earth impact is possible," according to Don Yeomans, manager of the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory.
Those in Eastern Europe, Asia or Australia will get the best telescope-aided view, scientists said. The asteroid won't be visible to the naked eye.
NASA spokesman Steve Cole told CNN that scientists had determined that the Russian meteor was on a very different trajectory from the asteroid.
"They are completely unrelated objects -- it's a strange coincidence they are happening at the same time," he said.
"This kind of object does fall fairly frequently, but when they fall into the ocean or desert, there is no impact on people -- so this one is unusual in the sense that it's come over a populated area."
Cole said he wasn't aware if scientists had foreseen the meteor's entry into the atmosphere.
Because meteoroids are smaller than asteroids or comets, they are hard to spot and there is often little warning that they are heading toward Earth, he said.
Colin Stuart, an astronomer at the Royal Observatory in London, said the asteroid's flyby Friday was a chance for experts to get an unusually close-up look and learn more.
"Scientists are going to fire radar beams off of the asteroid, trying to get an idea what it's made of and the how it's moving, so that in the future, if there's something that's a bit more of a threat to us, we have the best knowledge of what we are dealing with," Stuart said.
The asteroid, which is not connected to the Russian meteor, is not expected to hit any of the communications satellites it will pass on its trajectory, he said.
