A thirteen-year-old child was killed in Petrinja, the police said.
According to unofficial sources, the child is a girl.
For now there is no official information regarding injuries, however, it is expected to be available soon.
According to scenes in the field, the streets of Petrinja are full of debris and rescue workers are searching for survivors under the ruins.
About 20 people with injuries have been brought to the Sisak hospital, and two of them are in a serious condition, N1 television reported quoting hospital sources.
The earthquake has also damaged buildings in Zagreb, but there have not been any reports of any casualties in Zagreb, the head of the city's emergency services, Pavle Kalinic, has said.
The epicentre of the earthquake with a magnitude of 6.2 on the Richter scale that struck at 12.19 on Tuesday was in the town of Petrinja, some 60 kilometres southeast of Zagreb, the national seismology service reported, adding that extensive damage can be expected.
"The intensity at the epicentre of this devastating earthquake is estimated at VII-IX degrees on the EMS scale. The earthquake could be felt throughout Croatia. Extensive damage can be expected," the service tweeted.
The centre of the earthquake was at a depth of 10 kilometres, and its epicentre was 46 kilometres southeast of Zagreb in the town of Petrinja, located nine kilometres west-southwest of Sisak, the EMSC seismology service reported.
The EMSC estimates that about six million people felt the quake.
The US Geological Service (USGS) estimates that apart from Croatia the earthquake could be felt in Bosnia and Herzegovina, the Czech Republic, Germany, Hungary, Italy, Montenegro, Romania, Slovakia, Slovenia, Serbia and Austria.