Sri Lankans cast their votes yesterday in the closely fought presidential election. Although some problems were reported in the north of the island, in areas dominated by the Tamil minority, predictions of widespread violence were not realised and turnout was expected to be high.

The contest pits the incumbent, Mahinda Rajapaksa, against the former health minister Maithripala Sirisena, and is one of the most significant for decades.

Rajapaksa, who is seeking an unprecedented third term, called the elections early in the expectation of a comfortable victory. However Sirisena’s surprise candidature has united a fractured opposition.

With final tallies still being prepared, election officials estimated that participation reached more than 70% in most places in the first seven hours that the polls were open. Voting was unusually busy in the Tamil-dominated north and east of the country, which have boycotted national elections in the past, the officials said.

“A high turnout doesn’t favour the incumbent,” said Paikiasothy Saravanamuttu, of the Centre for Policy Alternatives in Colombo.

Election monitors have reported hundreds of irregularities during the campaign, and a 57-year-old opposition activist was killed in a drive-by shooting. The independent Centre for Monitoring Election Violence said it had documented more than 400 violent incidents since the election was announced on 20 November.

The monitors complained to the elections commissioner that bus drivers in the north-western Mannar district had stopped transporting voters to polling stations after a local ruling party politician told them not to. They also said illegal campaigning was carried out for Rajapaksa in the form of calls to boycott the polls, sent as text messages to ethnic Tamil voters who are expected to vote overwhelmingly in favour of Sirisena.

Results of the poll should be clear by Friday lunchtime, though counting may continue into the afternoon. There are concerns that the result, likely to be by a narrow margin, could bring weeks or months of chaos as supporters of either candidate try to win or keep power.

Rajapaksa, 69, is widely loathed by the country’s Tamils, 15% of the population, after overseeing a military campaign in 2009 which ended a 26-year civil war and destroyed the separatist Tamil Tigers.

The majority Sinhalese vote is split between Rajapaksa, who won enormous support with the military victory despite claims of human rights abuses by troops and thousands of civilian casualties, and 63-year-old Sirisena, who differs little ideologically but is seen as honest and capable.

“The president did what he promised by winning the war … he has shown results,” said Janaka Pradeep, a voter in Gampaha town, north of Colombo. “The opposition will only lead the country to chaos.”

However, Ranjith Abeysinghe, a taxi driver in the same town, said that although “big projects came … the poor struggle even to build a home” under Rajapaksa’s rule. “We need a change, we need a government that thinks about the poor,” Abeysinghe told the Associated Press.

South Asia’s longest-serving leader’s second term has been dogged by accusations of corruption, authoritarianism, and nepotism. Rising sectarian violence and inflation has also undermined popularity.

Pope Francis is scheduled to arrive in the country on Tuesday.