Persistent heavy rain caused the rivers, Korana and Kupa which run through the city, to overflow, flooding houses and roads and the city declared a state of emergency in the morning.
Croatian President Ivo Josipovic and Prime Minister Zoran Milanovic visited Karlovac where emergency services helped to evacuate the residents and a embankment along the Korana River was build.
Milanovic said "the whole of Croatia is in danger."
This is the second massive floods to hit the country in the last few months. In May over 1,000 people lost their homes as flooding devastated eastern Croatia.