Polls opened Sunday for tense elections in Thailand with opposition demonstrators preventing voting in parts of the country, a day after a gunfight between rival protesters in Bangkok raised fears of more violence.

The snap poll was called by Prime Minister Yingluck Shinawatra in an unsuccessful attempt to quell rising tensions in the nation, which has seen three months of sometimes bloody rallies aimed at toppling her government.

Protesters want the election delayed by a year or more so an unelected "people's council" can implement vaguely-defined reforms to expunge the influence of Yingluck's divisive brother Thaksin -- a former premier ousted in a 2006 coup that unleashed a cycle of political unrest in the country.

Voting could not go ahead in 45 out of the nation's 375 constituencies because of the actions of anti-government protesters, authorities said.

In the south, a stronghold of the anti-government movement, protesters stopped post offices from distributing ballot sheets and boxes to polling stations in 42 constituencies, said Election Commission secretary general Puchong Nutrawong.

In Bangkok polls were unable to be held in at least three constituencies, including in Lak Si -- the scene of a dramatic gun battle between pro-and anti-government protesters on Saturday which left at least seven people wounded.

But in some areas of the capital voting appeared to start without disruption by the opposition protesters, who have occupied key intersections in the city for a fortnight in a self-styled "shutdown" aimed at intensifying pressure on Yingluck's caretaker government.

Yingluck was among the early voters, casting her ballot in front of the media at a polling station in the capital.

At another polling station in the city's historic district, a trickle of voters turned out early Sunday watched over by a handful of police, according to AFP reporter at the scene.

"I did my duty today as I came to vote -- it's my right," said Pui, 43, giving one name.

"This year the election is chaotic," he added.

Clashes on Saturday night raised fears of more violence around the polls, with emotions running high on both sides of the political divide.

"It is very very important for leaders of both sides to completely reject violence... We cannot afford more casualties in Thailand," said Sunai Phasuk, a senior researcher with New York-based Human Rights Watch.

At least 10 people have been killed and hundreds injured in clashes, grenade attacks and drive-by shootings since the opposition rallies began.

Each side in the bitterly divided kingdom routinely blames the other for the violence.

The backdrop to the unrest is a long-running political struggle pitting Thailand's royalist establishment -- backed by the courts and the military -- against Thaksin, a billionaire tycoon-turned-politician who lives in Dubai to avoid a prison term for graft.

The recent violence is the worst political bloodshed in the kingdom since 2010 when protests by pro-Thaksin "Red Shirts" left more than 90 dead and nearly 1,900 injured in clashes and a military crackdown.

The elite-backed opposition Democrat Party -- which has not won an elected majority in around two decades -- is boycotting the vote.

This leaves the field open for Yingluck, who is expected to win the polls helped by strong electoral support among rural and urbanised communities from Thaksin's northeastern heartlands.

But disruption by demonstrators to candidate registrations means that if Yingluck wins she will still remain in a caretaker role with limited power over government policy until by-elections are held to ensure there are enough MPs to convene parliament.

Election officials have warned that the result may not be known for months because of problems caused by the protests.

Advance voting in parts of the country, including Bangkok, on January 26 was marred by blockades by opposition protesters who stopped hundreds of thousands of people from casting ballots.

Authorities said Saturday they were boosting security around the polls, with both police and soldiers on the capital's streets.

But the government has so far appeared reluctant to use force against the protesters, despite declaring a state of emergency last month.