Exit polls show Croatia's center-left opposition bloc winning Sunday's parliamentary elections by a wide margin, a victory that would break the long-dominant conservative grip on national politics in the Adriatic country.

A survey released shortly after polls closed showed the opposition coalition carrying more than 44 percent of the vote, against just more than 22 percent for the ruling Croatian Democratic Union. The Ipsos Puls agency survey was based on more than 25,000 voter interviews.

Election officials were quoted as saying 46 percent of the electorate had cast ballots three hours before polling stations closed.

Croatia is set to sign an accession treaty with the European Union later this week, keeping the country of 4.2 million on track to formally enter the debt-ravaged 27-nation bloc later this year. Whoever gains control of Croatia's 151-member parliament will face a spate of tough spending decisions aimed at easing the country's own economic downturn.

The conservative Croatian Democratic Union has ruled the country for all but two years since the 1990s war for independence from the former Yugoslav federation. But the HDZ has seen its popularity decline as it became embroiled in a series of corruption scandals, including its alleged involvement in illegal fundraising for previous elections.