"We won the parliamentary elections... The victory brought us responsibility to lead our country, which is in a difficult situation. Whoever wants to fight with us for the quality of life in Croatia is welcome," opposition leader Tomislav Karamarko of the HDZ party told cheering supporters.
The new government will be under pressure to push through much-needed reforms in Croatia as it slowly emerges from six years of recession, and oversee the transit of tens of thousands of migrants through the country of 4.2 million people.
"I believe that we will have a new prime minister designate soon," said President Kolinda Grabar-Kitarovic, who also hails from the HDZ.
New political party Most ("Bridge" in Croatian), was set to become a powerful force in national politics, coming third with 19 seats, although leader Bozo Petrov repeated a pre-electoral pledge that his party would not enter a coalition.
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The government led by Prime Minister Zoran Milanovic of the Social Democrats, elected in 2011, disappointed voters by failing to reform the public sector and boost the business climate, although Croatia saw a slight return to economic growth this year.
Defiant Milanovic called on Most to form a coalition with his centre-left bloc, telling his supporters: "We cannot go alone and we need partners."
Ahead of the vote, the premier appeared to have been buoyed by his handling of the migrant crisis, which has seen nearly 350,000 people passing through Croatia on their way to northern Europe since mid-September.