A meteor crashing in central Russia's Ural mountains has injured at least 500 people, as the shockwave blew out windows and rocked buildings.
Most of those hurt suffered minor cuts and bruises but some received head injuries, Russian officials report.
A fireball was seen streaking through the clear morning sky above the city of Yekaterinburg, followed by loud bangs.
The meteor is believed to have landed in a lake near Chebarkul, a town in the neighbouring Chelyabinsk region.
Much of the impact was felt in the city of Chelyabinsk, some 200km (125 miles) south of Yekaterinburg.
"It was quite extraordinary," Chelyabinsk resident Polina Zolotarevskaya told BBC News. "We saw a very bright light and then there was a kind of a track, white and yellow in the sky."
"The explosion was so strong that some windows in our building and in the buildings that are across the road and in the city in general, the windows broke."
Officials say a large meteor partially burned up in the lower atmosphere, resulting in fragments falling earthwards.
Thousands of rescue workers have been dispatched to the area to provide help to the injured, the emergencies ministry said.
The Chelyabinsk region, about 1,500km (930 miles) east of Moscow, is home to many factories, a nuclear power plant and the Mayak atomic waste storage and treatment centre.
Of 514 people injured in the Chelyabinsk region, 11 were being treated in hospital, the regional emergencies agency said in a statement.
Among those affected by the meteor were children, in school when it fell at around 09:20 (05:20 GMT).
Video posted online showed frightened, screaming youngsters at one Chelyabinsk school, where corridors were littered with broken glass.
"There was panic," Chelyabinsk resident Sergey Hametov told AP news agency by phone.
"We saw a big burst of light, then went outside to see what it was and we heard a really loud thundering sound. People had no idea what was happening. Everyone was going around to people's houses to check if they were okay."
Shockwaves were felt in a 19-storey building in the city centre, another witness said.
A roof at a zinc factory in Chelyabinsk also collapsed; however, it appears nobody was hurt in that incident.
In Yekaterinburg, 36-year-old resident Viktor Prokofiev was driving to work when he witnessed the event.
"It was quite dark, but it suddenly became as bright as if it was day," he was quoted by Reuters as saying.
Debris also reportedly fell on the west Siberian region of Tyumen.
The governor of Chelyabinsk region, Mikhail Yurevich, reported that the meteor had landed in a lake 1km outside Chebarkul, which has a population of 46,000.
Chelyabinsk city authorities said an initial blast had been heard at an altitude of 10,000m (32,800ft), suggesting it occurred when the meteor entered Earth's atmosphere, Reuters reports.
Such meteor strikes are rare but one is thought to have devastated an area of more than 2,000 sq km (1,250m) in Siberia in 1908.
That event smashed windows as far as 200 km (125 miles) from the point of impact.
Scientists have played down suggestions that there is any link between the event in the Urals and 2012 DA14, an asteroid expected to race past the Earth on Friday at a distance of just 27,700km (17,200 miles) - the closest ever predicted for an object of that size.
Prof Alan Fitzsimmons, of the Astrophysics Research Centre at Queen's University Belfast, said there was "almost definitely" no connection.
"One reason is that 2012 DA14 is approaching Earth from the south, and this object hit in the northern hemisphere," he told BBC News.
"This is literally a cosmic coincidence, although a spectacular one."