It was the worst shooting attack in the young country's history.
The gunman was a local man aged around 60, said Patrik Kuncar, mayor of the southeastern town of Uhersky Brod.
Czech public radio said the gunman called a local television station before the attack, complaining that police were not solving his problems and threatening that he would "take things into his hands."
Interior Minister Milan Chovanec, who arrived at the scene, said the man had a gun license. "It was not a terrorist attack" he said.
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The Czech Republic became an independent nation in 1993 after the split of Czechoslovakia.
The attack shocked the town of 17,000 that lies 300 kilometers southeast of Prague, the capital, and is home to the Ceska Zbrojovka gun plant.
"Nobody believed anything like that could happen in such a small town," Kuncar said. "I can hardly imagine what consequences it will have for the future life in this town." The victims have been identified and were all from the region, Chovanec said.
The country's chief police officer, Tomas Tuhy, said authorities would not reveal more information immediately because of the ongoing investigation.
The Czech Republic has strict gun control laws, but hunting is popular in the eastern European nation.
"I am shocked by the tragic attack in Uhersky Brod," Prime Minister Bohuslav Sobotka said in a statement while on a trip to South Korea. He offered his condolences to the victims' relatives and President Milos Zeman did the same.
In a tragedy of a similar scope in the then-communist Czechoslovakia, a female truck driver intentionally hit a group of people waiting for a tram in Prague in 1973, killing eight. She was later executed.