Travellers from Serbia, Bosnia, North Macedonia and Kosovo will have to self-isolate upon arrival in the country.
Croatia has reimposed quarantine for visitors from its four Balkan neighbours following a second wave of coronavirus in the region.
Travellers from Bosnia, Serbia, Kosovo and North Macedonia will all have to self-isolate for 14 days upon arrival in Croatia. Transit travellers will be exempted, Croatian Interior Minister Davor Bozinovic told reporters.
In late May, Croatia opened its borders to ten EU countries, including Germany, Austria and Estonia.
The country had recorded few or no infections at all since mid-May, but the situation worsened last week, when Croatia began to report up to 30 new COVID-19 cases a day.
The outbreak coincided with a leg of the international tennis charity tournament Adria Tour organised in the coastal town of Zadar on June 20.
After the event, Novak Djokovic, the organiser, his wife, and other three tennis players tested positive for coronavirus.
The tour had kicked off in Belgrade, in what news agency AFP reported to be a crowded stadium.
After Djokovic tested positive, the Croatian prime minister Andrej Plenkovic came under fire for not self-isolating as he patted Djokovic's shoulder at the tournament. Plenkovic later tested negative for coronavirus.
Serbia has also been struggling to contain the outbreak. Authorities on Wednesday reported 143 new cases - only one day after imposing face-mask on public transport.
The country had relatively loose lockdown measures and last weekend held Europe's first national election since the beginning of the pandemic.
Bosnia, North Macedonia and Kosovo too all recorded a higher infection rate since the beginning of June, with up to nearly 200 new cases a day in North Macedonia.
In Bosnia, the number of new cases registered in June accounted for a third of all cases confirmed in the country, while in Kosovo, the government warned it may have to reinstate some economically-damaging lockdown measures after a rise in the number of infections in the past three weeks.
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