Djukanovic is the most high-profile of the seven candidates, with posters plastered all over the capital Podgorica - where a third of Montenegro's population lives - proclaiming him as "leader, statesman and president of all citizens".
With 80 per cent of ballots counted, the Center for Monitoring and Research said on Sunday that Djukanovic had won about 53 per cent of the vote, ahead of his main opponent Mladen Bojanic with 34 per cent. None of the remaining six candidates reached double digits.
Montenegro's former Prime Minister and former President Milo Djukanovic, the leader of the ruling Democratic Party of Socialists, has claimed to have won the Sunday presidential election and pledged to ensure the country's European Union membership before the end of his five-year presidential term.
"After this overwhelming and superior result you should reconsider your political position", he said in a direct message to opposition leaders.
About 530,000 voters were choosing among several candidates in the Adriatic Sea nation that used to be part of Yugoslavia.
Montenegro's State Election Commission is expected to announce the final results of the presidential election within the next few days.
Mr Djukanovic has dominated politics in the former Yugoslav republic for nearly 25 years and stepped down as prime minister in 2016.
Mladen Bojanic was Djukanovic's main rival, having been put forward by the leading opposition party, the Democratic Front, which prefers closer ties to Russian Federation and accuses Djukanovic of both nepotism and corruption.
The opposition accuses Djukanovic of being linked to the mafia, which he denies.
The issue of organised crime cast a shadow on the campaign, with some 20 people killed by assassination or auto bombs over the last two years.
Mr Bojanic said Mr Djukanovic "cannot be the solution because he is the creator of the instability and chaos that we witness in the streets of Montenegro".
Bojanic conceded defeat, saying: "Montenegro chose the way it chose". The average salary in Montenegro sits at around €500 ($615) and unemployment is more than 20 percent.
The EU in its 2016 progress report told the country it should continue its efforts to reduce organised crime, especially human trafficking and money laundering.
While Sunday's presidential election was less tense, CEMI and another monitoring group, CDT, reported numerous irregularities at dozens of polling stations.
- What to expect from severe weather Sunday in SC
- Manchester City clinches 2017-18 Premier League title
- Injured Broncos cheered by Stanley Cup visit to their hospital bedsides
- 35-year-old pregnant woman in Uttar Pradesh gangraped by 4
- Trump Lawyer Cohen Reportedly Seeking Restraining Order Over FBI Raids
- British-French join hands in operation against Syria's chemical weapons
- Meghan Markle flies to Chicago to finalize visa application
- Punjabi Pop Singer Parmish Verma Shot at in Mohali, admitted to hospital
- Merkel endorsed the impact of the United States and its allies on Syria
- EU Brexit negotiator: No Irish border breakthrough for weeks