The Czech Republic finds itself "in a very difficult situation again" Prime Minister Andrej Babis told the nation in a special address on Monday night, adding "the epidemic is back".
The country is now ranked second worst in the EU in terms of daily growth in cases, Interior Minister Jan Hamacek said.
The country had managed to avoid the worst of the pandemic by swiftly imposing a lockdown in the spring - thousands of Czechs even attended a "farewell party" for the pandemic in central Prague in July.
But a further 1,476 infections were confirmed on Monday, bringing the total to 50,764 in the nation of 10 million people.
Mr Babis said it was a mistake to lift restrictions in the summer. "Even I got carried away by the coming summer and the general mood. That was a mistake I don't want to make again," he said. However he said he did not want to introduce the same wide-ranging measures, and called on Czechs to act responsibly.
Hundreds of people enjoy a concert on a floating stage on the Vltava river on September 19, 2020, in Prague, Czech Republic.