Torrential rain has caused rivers to break their banks in central Europe leaving towns and cities under several feet of water.
Parts of the Czech Republic, Germany, Austria, Hungary and Poland have reported serious flooding, with water levels reaching record highs.
The Czech government has drafted in 300 soldiers to help bolster flood defences after the river Vltava broke its banks.
Local media cited the head of Hungary's National Disaster Authority as saying that water levels in the Danube could exceed the height seen in the record flooding in 2002.
The town of Passau in southern Germany is seeing some of the worst flooding in 70 years.
Czech Prime Minister Petr Necas pledged 300 million Czech crowns ($15 million) to relief efforts and said another 2,000 troops were ready to support the 300 soldiers already helping to erect temporary barriers and pile sandbags in Prague and other areas.
"The government approved the declaration of a state of emergency, which will enable a more effective rescue effort," said Necas after an emergency cabinet meeting, adding that there was another 1.3 billion crowns available to help fund the cleanup operation.
The historic area of Prague is a UNESCO heritage site boasting hundreds of well-preserved buildings, churches and monuments dating back centuries, including the Charles Bridge straddling the Vltava that was closed due to high water
Czech Prime Minister Petr Necas declared a state of emergency for most of the nation on Sunday as swollen rivers caused by days of heavy rain threatened Prague's historic centre and forced evacuations from low-lying areas.
Prague authorities limited public transport and planned to close underground stations in the centre of the city as water from the Vltava River overflowed into picturesque areas popular with tourists
The main train line connecting the capital and the east of the country was also shut.
Footage of the building and surrounding area affected by a powerful blast in the Czech capital Prague, which injured up to 40 people.
It is not certain what caused the explosion but a police spokesman has said it is likely to be natural gas.
Emergency workers are searching the building for any people buried under the rubble.
Emergency workers are continuing to search an office building in the Czech capital in Prague after a powerful explosion earlier today.
Several people are missing and authorities believe there is a possibility that people could be buried under the rubble.
Pavlina Adamcova, a spokeswomen for the fire service, said sniffer dogs were being used to help the search.
Sniffer dogs searching a building after a strong blast in central Prague have not yet found anyone at the scene.
Earlier, a fire services spokesman said that some people could be trapped under the rubble.
Two people are believed to be missing, but they may have left before the explosion, Czech newspaper Ceskenoviny reports, citing a police spokesman.
An eyewitness has described her shock after the an explosion at a building in the Czech capital of Prague.
Venceslava Sehnotkova 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".
Up to 40 people are believed to have been injured in the blast which is suspected to have been caused by gas, a police spokesman has said.
Emergency services are searching the building - which belongs to the Czech Air Navigation Services company - for people who may have been trapped.
In a statement, the Prime Minister of the Czech Republic Petr Necas said he was "deeply hit by the tragedy of the gas explosion", the Associated Press reports.
It is not certain what caused the blast in Divadelni Street in the central Prague but it was likely to be a natural gas explosion, police spokesman Tomas Hulan said.
Emergency services are attending to the scene of a powerful explosion in central Prague.
Zdenek Schwarz, the head of the rescue service, has said that up to 40 people have been injured.
One eyewitness said: "There was glass everywhere, some people shouting and crying".
A police spokesman said a blast in the Czech capital Prague was probably caused by gas and that there had been about 15 people in the building.
There have not been reports of any deaths, a fire department spokeswoman said.
The explosion, close to Prague's National Theatre, was heard as far as Prague Castle about a mile away.
Windows in neighbouring buildings were blown out, including Prague's landmark Cafe Slavia.