A powerful explosion in the centre of Prague has injured up to 40 people and left several others buried under rubble, police have said.
The blast in a building on Divadelni Street, close to the National Theatre, was heard as far away as Prague Castle, over a mile away across the Vltava river.
It blew out the windows on many of the surrounding buildings which were evacuated.
Zdenek Schwarz, head of the rescue service in Prague, said up to 40 people have been injured but mainly suffered bruises and cuts from glass.
Prague emergency service spokeswoman Jirina Ernestova said there were fears three people may be buried in the rubble of the damaged building which police said was a former block of flats now used as office space.
Sniffer dogs were being used and Ms Ernestova said ambulances were staying at the scene "in case someone was pulled out of the rubble".
A police spokesman said the explosion was probably caused by natural gas and that there had been around 15 people in the building, which included an office of the International Air Transport Association (IATA) and an art gallery.
Pensioner Venceslava Sehnotkova, who lives in a nearby house, told Reuters: "I was sitting quietly in my flat, making coffee. Then there was an incredible explosion. I thought the building would collapse.
"I looked out the window, and there was only dust everywhere."
Students and teachers from two nearby universities panicked and ran out when the blast shook their buildings, fearing a terrorist attack, an unnamed student told Czech TV.
"I was in the bathroom, no windows, the door was closed, honestly, if I had been in my bed I would have been covered in glass," said Z B Haislip, a student from the US.
Prime Minister Petr Necas said in a statement he was "deeply hit by the tragedy of the gas explosion".