Montenegrin voters easily cleared the first hurdle for a valid independence referendum on Sunday, by surpassing the required 50 percent turnout threshold in the first few hours of a ballot on whether to dissolve their union with Serbia.
If more than 55 percent of the electorate say "Yes" to independence, the mountainous Adriatic republic will become Europe's newest state. The criteria were agreed with the European Union, which Montenegro hopes to join.
"As of 1 p.m. our observers calculate that 51.8 percent of voters have exercised their right to cast a vote," said an official of the Centre for Democratic Transition (CDT), one of the groups monitoring the referendum.
Voting was due to end at 9 p.m. (8 p.m. Irish time).
There was little doubt ahead of the poll that the pro-independence camp would emerge stronger. The question for Montenegro's future was whether the "No" vote could deprive them of the 55 percent majority.
Turnout was heaviest in the north, mostly populated by ethnic Serbs expected to reject a break with Serbia, monitors said. There were no reports of trouble.
"This is a big day for Montenegro," said pro-independence champion Milo Djukanovic, the country's prime minister and former president. "Its answer to the referendum question will open the doors to Euro-Atlantic integration."
Queues formed early at polling stations in downtown Podgorica, the provincial-looking capital of the mountainous state. Elderly men dressed in their Sunday best filled in pink voting slips which asked simply: "Do you want Montenegro to be an independent state?" Answer yes or no
The union of Serbia-Montenegro, the last vestige of the former Yugoslavia, was created in 2003, but its two republics have been in some form of joint state for almost a century.