The Centre for Monitoring Election Violence (CMEV) reported 160 incidents of poll-related violence during the first four hours of balloting across the country.
A shoot-out between a group of opposition and government supporters in the island's south early Thursday damaged a vehicle, but caused no injuries, CMEV spokesman D.
M. Dissanayake said.
Most complaints were against the ruling United People's Freedom Alliance led by President Mahinda Rajapakse.
"Pro-government supporters are reported to have intimidated voters," Dissanayake said, adding that in some places unidentified men had grabbed polling cards from those trying to cast their ballots.
He said dozens of war-displaced people in state-run makeshift shelters were without transport to get to polling booths.
The private People's Action for Free and Fair Elections reported cases of pro-government supporters chasing away polling agents belonging to opposition parties.
More than 14 million people are eligible to