Fresh tremors shook Croatia on Wednesday as the Adriatic country was still picking up the pieces of a deadly earthquake that claimed seven lives and reduced buildings to rubble the day before.

Search efforts for survivors stretched into the night Tuesday after a powerful earthquake killed at least six people in central Croatia, tearing down rooftops and piling rubble in the streets.

Croatian police launched a manhunt Thursday after six people were found shot dead inside a house in the capital Zagreb, police said. 

Croatia's conservatives were poised to remain in power after winning a snap election, nearly complete results showed Monday, but will have to begin coalition talks to form a government after falling short of a majority.

Croatians began voting Sunday in a snap election whose outcome might prolong political uncertainty in the EU's newest member, which had shifted to the right under previous conservative governments.

The main party in Croatia's fragile ruling coalition announced Tuesday it would file a no-confidence vote against Prime Minister Tihomir Oreskovic, in a move likely to lead to snap elections.

After weeks of political turmoil, the conservative HDZ party announced it would seeking the motion against Oreskovic, a non-partisan premier who came to power in January.

Croatia's President Kolinda Grabar-Kitarovic on Wednesday demanded the EU implement a clear policy on migrants as she and two other Balkan heads of state visited a flashpoint area on the Greece-Macedonia border.

"EU should be clear in its policy towards migrants and take care of those who have the right to asylum, who are fleeing war," Grabar-Kitarovic said after visiting a reception center in Gevgelija on Macedonia's southeastern border with Greece.

U.N. war crimes judges have ordered an indefinite halt to the trial of Croatian Serb rebel leader Goran Hadzic who is suffering from brain cancer, according to a ruling released Tuesday.

In a majority decision, the judges at the International Criminal Tribunal for the former Yugoslavia (ICTY) found that Hadzic "is currently unfit to stand trial".

European Union member Croatia is from Friday limiting the number of migrants entering the country to 580 a day, following a similar decision from neighboring Slovenia, a police spokeswoman told AFP.

"Slovenia informed us on Thursday evening that they can receive 580 migrants daily and we have informed our colleagues in Serbia about it. We will stick to that figure also," Croatian police spokeswoman Jelena Bikic said.

Bosnian police on Wednesday arrested five wartime officers and an ex-politician, all ethnic Serbs, suspected of involvement in the deaths of hundreds of civilians during the country's 1990s conflict.

"These people are suspected of implementing, as senior military officials... the expulsion of some 5,000 Muslim and Croat civilians from Kotor Varos," a northwestern town, the prosecutor's office said in a statement.