In Zagreb, the incumbent Mayor Milan Bandic of the Bandic Milan 365 - Work and Solidarity Party won 39.69 percent of the vote, ahead of Anka Mrak Taritas, the candidate of the Croatian People's Party (HNS) backed by the Social Democratic Party and several smaller parties, who received 21.01 percent.
In Split, Zeljko Kerum of the Croatian Civic Party (HGS) captured 32.43 percent and Andro Krstulovic Opara of the Croatian Democratic Union (HDZ) took 24.81 percent.
In Rijeka, the incumbent Mayor Vojko Obersnel of the SDP, supported by six other parties, leads with 40.62 percent, followed by independent candidate Hrvoje Buric on 16.34 percent.
In Osijek, the current Mayor Ivan Vrkic (independent) won 36.21 percent, ahead of the HDZ's Ivana Sojat on 16.73 percent.
Runoff elections will be held on June 4.
Mayors, county prefects and their deputies are elected by the proportional electoral system, and each municipality, city or county makes one constituency.
A candidate who receives more than 50% of the vote is elected mayor or county prefect. If no candidate receives the required majority in the first round, the first two vote-getters face off in a runoff in two weeks' time.