The announcement came after a meeting of a government crisis management team and a day after the country moved to institute sanitary checks at ports, on trains and at four border crossings with Germany and one with the Czech Republic.
Health Minister Łukasz Szumowski said at a joint press conference with Prime Minister Mateusz Morawiecki on Tuesday that Poland had 18 cases of the new coronavirus. No deaths had been reported as of mid-morning Tuesday.
The first case of coronavirus infection was reported in Poland last week.
The sports ministry said on Tuesday it was recommending that all sporting events in the country should be cancelled.
Meanwhile, President Andrzej Duda has vowed not to hold large public gatherings as part of his re-election campaign in order to avoid spreading the virus. Poland’s presidential elections are due to take place on May 10, with a potential second round scheduled for May 24.
On Monday afternoon, the Polish health ministry reported that 467 people with suspected coronavirus infection were in hospitals nationwide, with a further 1,014 quarantined and 7,110 under epidemiological supervision.
Poland’s top Ekstraklasa football league said that matches would be played behind closed doors, without supporters.
The Medical University of Warsaw announced it was cancelling lectures for students and suspending visits by foreign guests.
And the authorities in the western city of Poznań said they were closing local schools, kindergartens, zoos, swimming pools and cultural centres for two weeks.
Under special rules that came into force in Poland on Sunday, people suffering from or suspected to have an infectious disease can be ordered to undergo treatment in hospital.
The new SARS-CoV-2 coronavirus, which causes a disease called Covid-19, was first reported in Wuhan, China. It has now spread to more than 100 countries.
The most common symptoms of the illness are fever, coughing, difficulty in breathing, muscle pain and fatigue.