Explosions and heavy gunfire have rattled Bangkok as pro- and anti-government protesters clashed on the eve of Thai elections seen as unlikely to end a cycle of violence in the kingdom after months of opposition rallies.

Tensions are high in the capital ahead of snap elections on Sunday, which opposition demonstrators have vowed to block as they seek to prevent the likely re-election of Prime Minister Yingluck Shinawatra.

At least seven people were wounded, including an American photojournalist in the gun battle.

One person was seen wounded by a gunshot and two were injured by explosions in the northern Laksi area, close to the Don Muang airport and a stronghold of Yingluck's Puea Thai Party.

The confrontation began after a group of pro-government supporters marched to a district office containing ballot boxes that had been surrounded by protesters.

"The clash point is the intersection, gun shots seemed to be fired from both sides," said Sunai Phasuk, a senior researcher with New York-based Human Rights Watch, who was at the scene.

"This election is not so much about who wins and loses votes. What it’s more about how many Thai people make a point in exercising their right to vote," Al Jazeera's Veronica Pedrosa, reporting from Bangkok, said.

Calls for peace

Thousands joined Saturday's protests for and against against Yingluck, and her decision to push ahead with the election despite official advice to postpone polling in the face of unrest.

Suthep Thaugsuban, a former MP and minister who leads the protests against Yingluck's party, had earlier called for a peaceful blockade of roads to disrupt the election, but has also vowed not to stop people from voting.

"The people will not close the polling booths, but will demonstrate on the roads. They will demonstrate calmly, peacefully, without violence. We won't do anything that will hinder people from going to vote," Suthep said on Friday.

"In the south, for those who are surrounding the places where ballots are being collected, I ask that you sit there peacefully. Don't back down. I believe that this poll will be voided for sure."

The Nation newspaper said protesters were camping at post offices to block the delivery of ballot papers in the south, where support for Suthep is strongest.

Many protesters in Bangkok wore red - the colour of Yingluck's "red shirt" supporters - in Saturday's march, after Suthep said no one had the right to hijack a colour.

"In honour of Chinese New Year, let's wear red on our walk in Yaowaraj (Chinatown)," said Suthep, himself wearing a red shirt.

Rival protests

Pro-government supporters were also holding rallies. Al Jazeera's Pedrosa said that some people were viewing the tensions as "pro-election versus anti-election" rather than opposition and pro-government.

"We want to protect Thailand's democratic system. We won't let those anti-election people disrupt those who want to vote. They shouldn't be deprived from voting," said Yodsawarid Chuklom, a leading Yingluck supporter.

Ten people have died and at least 577 have been wounded in politically related violence since late November, according to the Erawan Medical Center, which monitors Bangkok hospitals.

The anti-government protesters took to the streets in November in the latest round of an eight-year conflict between Bangkok's middle class, southern Thais and the royalist establishment against the mostly poor, rural supporters of Yingluck and her brother, the former prime minister Thaksin Shinawatra, who was toppled by a protest movement in 2006.