The quake, which according to the GFZ German Research Centre for Geosciences struck at a shallow depth of just 10 kilometres, was felt in all of Croatia's neighbours, including in the Hungarian capital Budapest, and as far as southern Germany.
The epicentre was 50km south of the Croatian capital Zagreb.
According to the Croatian Red Cross, there was a "very serious" situation in the town of Petrinja, where a large number of buildings have been damaged. The same area was struck by a 5.2 quake on Monday.
"Hundreds of people who were forced to leave their homes are accommodated in communal buildings and tents, while others are seeking shelter in different parts of the country, increasing the risk of transmission", a statement said.
N1 quoted a Petrinja town official as saying that a 12-year old child in Petrinja had been killed, but gave no details.
"The center of Petrinja as it used to be no longer exists", says Croatian state broadcaster, HRT, of the disaster.
"My town has been completely destroyed". Local media reported that the man was the church's organist.
The quake was felt in Sarajevo and Belgrade.
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"It was disgusting, a shock".
Today, Vice-President of the European Commission Dubravka Šuica and the European Commissioner for Crisis Management Janez Lenarčič arrived in Zagreb, Croatia where they met with Prime Minister Andrej Plenković.
The army is assisting with rescue efforts, and Plenkovic said there were places for 500 people to sleep in barracks.
Civil Protection director Damir Trut said on Friday morning that a thousand people were in Sisak-Moslavina County, helping its residents clear streets of rubble following the natural disaster that hit the county on December 29. Earlier in the week, the Commission's chief, Ursula von der Leyen had tweeted that the European Union was standing "ready to support", Croatia, adding that she would ask the bloc's Crisis Commissioner to travel to the country "as soon as the situation allows".
Health officials said a baby was delivered in a tent in front of the hospital in the aftermath of the natural disaster.
Atalic said that it was too early to say how many houses would have to be torn down.
He stressed that all patients from the hospital in Petrinja and most from nearby Sisak were being taken care of and transferred to Zagreb. It was felt as far away as Graz in southern Austria, the Austria Press Agency reported.