A suspected gas explosion has damaged an office building in the centre of the Czech capital Prague injuring up to 35 people and sending shockwaves through the Old Town tourist district.
Initial agency reports suggest that some people may be trapped in debris following the explosion in Divadelni Street.
Police have sealed off the area around the blast.
Windows in buildings located hundreds of yards from the incident, including some in the nearby National Theatre, were shattered.
A police spokesman said the blast was probably caused by gas and that there had been about 15 people in the building, which included an office of the International Air Transport Association (IATA) and an art gallery. There has been no official confirmation of the cause of the explosion.
The explosion was heard as far as Prague Castle about a mile (1.6 km) across the Vltava river.
"There is an unknown number of injured and trapped people," said Jirina Fikejzova, Prague emergency services spokeswoman.
A Reuters witness at the site said about a dozen people were being treated by emergency services.
Firefighters spokeswoman Pavlina Adamcova said rescuers were still searching the rubble, using sniffer dogs.
The blast blew out windows in neighbouring buildings, including Prague's landmark Cafe Slavia.
A fire department spokeswoman said there have not been reports of any deaths.
Neighbouring buildings were being evacuated, the spokeswoman said.
Prime Minister Petr Necas said in a statement he was "deeply hit by the tragedy of the gas explosion."