Croatia's ruling center-left coalition faces a strong challenge from a conservative opposition in the Balkan country's first parliamentary election since joining the European Union in 2013.

The outcome of the vote Sunday could disrupt the flow of tens of thousands of migrants crossing the small country if the conservatives return to power and implement tough measures against the surge.

Neither the conservatives, led by former intelligence chief Tomislav Karamarko, nor the left-wing coalition, led by incumbent Prime Minister Zoran Milanovic, are expected to win an outright majority. The forming of the new government will depend on several small parties that are expected to enter the 151-seat parliament.

Croatia, with a population of 4.2 million, is one of the EU's poorest countries and both camps have pledged to revive the economy.