Divers scoured the bottom of a Russian lake Saturday for fragments of a meteorite that plunged to Earth in a blinding fireball whose shockwave hurt 1,200 people and damaged thousands of homes.
The 10-tonne meteor streaked over the Ural Mountains on Friday just as the world braced for a close encounter with a large asteroid, leaving some Russian officials calling for the creation of a global system of space object defence.
The unpredicted meteor strike ground traffic to a halt in the industrial city of Chelyabinsk as residents poured on to the streets to watch the light show before scrambling for safety when a glass-shattering sonic boom rang out directly overhead.
Some 37 adults and three children remained hospitalised with cuts and some more serious injuries on Saturday afternoon.
A massive force of 20,000 recovery workers was busy Saturday patching up windows with plastic sheeting and checking 3,000 buildings for cracks amid temperatures near a blisteringly cold -20 degrees Celsius (-4 degrees Fahrenheit) overnight.
Police meanwhile patrolled the streets for marauders who threatened to take advantage of the broken storefronts that lined Chelyabinsk's main streets.
"We have taken all the facilities under our control," district police chief Marat Minzagirov told Russian state television as night fell on the city of 1.1 million.
A piece of the meteor -- called a meteorite once it hits the ground -- was believed to have plunged into the region's frozen Lake Chebarkul and possibly a few other locations.
But the six divers who searched its waters for three hours on Saturday were able to finding nothing but mud and silt.
"They immediately discovered that the water's visibility was zero and that the bottom was covered with 1.5 metres (five feet) of sticky mud," a recovery team member told Russian media.
Yet meteor hunters appeared unbowed and several Russian websites carried ads offering as much as 300,000 rubles ($10,000) for an authentic piece of the latest space rock to hit the planet.
A few sites even offered pecular-shaped rocks for sale, but scientists cautioned that none were likely to be the genuine article.
The meteor explosion is the most stunning cosmic incident above Russia since the 1908 Tunguska Event, in which a colossal blast most scientists blame on an asteroid or a comet levelled trees across a stretch of Siberia.
Scientists at US space agency NASA estimated that the amount of energy released in the atmosphere Friday was about 30 times greater than the force of the nuclear bomb dropped on the Japanese city of Hiroshima during World War II.
"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 Programme Office.
"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," he said in a statement published on the NASA website.
The drama in Russia developed just hours before an asteroid -- a space object similar to a tiny planet orbiting the sun -- whizzed safely past Earth at the unprecedented distance of 27,000 kilometers (17,200 miles).
That put it closer to the earth then some distant satellites and set off alarm bells in some Russian circles, with some saying the time had come for joint global action on the space safety front.
"Instead of fighting on Earth, people should be creating a joint system of asteroid defence," the Russian parliament's foreign affairs committee chief, Alexei Pushkov, wrote on his Twitter account late Friday.
"Instead of creating a (military) European space defence system, the United States should join us and China in creating the AADS -- the Anti-Asteroid Defence System," the close ally of President Vladimir Putin wrote.
NASA estimates that a smallish asteroid such as the 2012 DA 14 flies close to Earth every 40 years on average while only hitting the planet once every 1,200 years.