According to the exit polls which the nongovernmental organisation, called Centre for Democratic Transition carried out, 56.3 percent of Montenegrins who went to the polls voted for the independence of this mountainous Adriatic republic from the state union with Serbia.
The referendum saw a high turnout of 86.6 percent of 484,718 eligible voters.
Montenegro with a population of over 620,000 began celebrating the victory of the pro-independence bloc immediately after nongovernmental organisations presented preliminary projections of the referendum.
Later on Sunday evening, the NGOs said that the figure was revised down from the initial 56.3 per cent to 55.4 percent, the dpa news agency reported quoting an analyst as saying that the figure "was stable" above the 55 per cent threshold set by the referendum law.
However, the pro-union bloc refused to accept the defeat. At a news conference on Sunday evening, the head of that bloc, Predrag Bulatovic, condemned the celebrations and fireworks displays in Podgorica's streets and throughout the country. He called on citizens to stay calm and tolerant and wait for the announcement of official results by the Montenegrin Referendum Commission.
The Commission is expected to publish first official returns on Monday morning.
The head of the pro-independence bloc, Montenegrin Prime Minister Milo Djukanovic, is due to hold a news conference later on Sunday evening.
The European Union helped broker the main rules for the organisation of the referendum. The key rule was the requirement that at least 55 percent of votes need to be cast for independence. The other requirement was that at least 50 percent of registered voters would turn out for the referendum.
Earlier on Sunday, the head of the Montenegrin Referendum Commission, Francisek Lipka, said that the process of voting was proceeding smoothly and without any major problem. The media and NGOs also reported that there were no serious irregularities which could have undermined the referendum.
On Sunday before the closing of the polling stations, Montenegrin leaders and local religious dignitaries expressed their strong conviction that over 55 percent of voters would vote for the independence.
A total of 1,020 polling stations opened at 0800 hrs throughout the country and closed at 2100 hours. The voting was overseen by more than 3,500 monitors, nearly 700 of them from abroad.
The referendum was covered by several hundreds reporters and nearly 200 of them were journalists from the foreign media.
An advisor of Serbian Prime Minister Vojislav Kostunica, was quoted by the Television B92 in Belgrade that everybody would accept the final outcome of the referendum, no matter whether it is for Montenegro's independence or for the preservation of the state union with Serbia.
Serbian electronic media were covering the developments in Montenegro all the Sunday evening.