Space object explodes over Russia, injuring 1,100 MOSCOW - Without warning, a celestial object that NASA described as a "tiny asteroid" streaked above Russia's Ural Mountains early Friday before exploding, creating a shock wave that rattled buildings, shattered glass and injured hundreds of people. Many witnesses in Chelyabinsk said they saw a white trail across the sky and a bright flash and heard a loud explosion seconds before buildings in the eastern part of the city were jolted. Scientists said it was the largest such event in more than a century, since a blast that leveled 800 square miles of forest in 1908, the so-called Tunguska event, also in Siberia. Its occurrence on Friday, hours before scientists were anticipating the close flyby of a larger asteroid, known as 2012 DA14, marked an extraordinary coincidence. Scientists said the two events were not related. "When I saw some white narrow cloud moving outside the window, I ran up to it and saw a huge blinding flash," Nadezhda Golovko, deputy head of Chelyabinsk Secondary School No. 130, said in a phone interview. It was the way I would imagine a nuclear bomb. At first, there was no sound at all, as if I suddenly went deaf. Then I started hearing loud sounds of something exploding, four or five, one after another, and then the school windows started breaking," she said. More than 1,100 people had been treated for injuries by late Friday, with about 50 hospitalized, Marina Moskvicheva, a spokeswoman for the Chelyabinsk regional health department, told Interfax. U.S. scientists estimated that the object measured about 45 feet across, weighed about 10,000 tons and was traveling about 40,000 mph. It exploded about 15 miles above the surface, causing a shock wave that triggered the global network of listening devices that was established to detect nuclear test explosions. The force of the explosion was between 300 and 500 kilotons, equivalent to a modern nuclear bomb, according to Bill Cooke, head of the Meteoroid Environment Office at NASA's Marshall Space Flight Center in Huntsville, Ala. NASA scientists believe the object originated from the asteroid belt, a vast collection of debris orbiting between Mars and Jupiter that consists of leftover bits from the formation of the solar system. It probably traveled for a year before it burst into the atmosphere Friday. Russian officials said the object, which they called a meteor, apparently entered the atmosphere over the north of Kazakhstan and flew over part of Russia before exploding over Chelyabinsk. "We have deployed 28 stations in the area to monitor radiation levels, which up to now remain normal," said Vladimir Stepanov, chief of the Emergency Situations Ministry's crisis center. He said that officials did not have sufficient time to issue a warning before the object entered the atmosphere. The biggest piece to make it all the way to the ground was believed to have fallen into Chebarkul Lake about 60 miles west of Chelyabinsk, according to Russia-24, a government news television network. It showed video of a 24-foot-wide hole in the lake's thick ice. Truck driver Andrei Chernov, who was heading to Chelyabinsk from nearby Kopeysk shortly after 9 a.m., said he saw what he thought was "a huge ball of fire silently rising all over Chelyabinsk." "I thought some catastrophe was happening in the city," he said. I started dialing my wife, but there was no connection. Dozens of witnesses posted videos and photos to the Internet. Russia-24 aired images of the destruction at an indoor athletic stadium in Chelyabinsk, where at least two people were seen covered with blood among the debris. No one was killed, the report said. Mikhail Yurevich, the regional governor of Chelyabinsk, estimated that the material damage had exceeded $33 million, Interfax reported.