The earthquake, which was felt throughout the country as well as in neighboring Serbia, Bosnia and Herzegovina, caused serious damage to buildings in Petrinja, a town southeast of the capital Zagreb.
The half of the train station fell apart, people were falling down and the train could not stop in the town, an eyewitness said.
The officials urged people to not make any call except for urgent matters, only use texto to help rescue operations.
Three foreshocks had hit the same area the day before, estimated by the Croatian Seismological Service (CSS) at magnitudes 5.0, 4.7 and 4.1 respectively.