Violence erupted in Bangkok on the eve of tense Thai elections, with explosions and heavy gunfire breaking out in clashes between pro- and anti-government protesters.

People raced for cover in a shopping mall after a man pulled an assault rifle from a bag and began spraying bullets during a stand-off between government supporters and scores of opposition demonstrators.

The shooting went on for at least one hour.

Emergency workers said several people were injured in the fighting, which broke out as anti-government groups laid siege to a ballot box distribution centre in the Thai capital.

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

Bangkok has been rocked by weeks of sometimes bloody rallies by a loose coalition opposed to Ms Yingluck and the enduring influence of her brother Thaksin Shinawatra -  a former premier ousted by the military in 2006.

The unrest is the latest round of political instability to hit Thailand since royalist generals ousted Mr Thaksin seven years ago.

Today's clashes happened after demonstrators blocked ballot boxes from being delivered from the Lak Si district office in northern Bangkok.

At least two explosions were heard in the area, which police attributed to Molotov cocktails, before the firing began.  

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

Observers are predicting a chaotic election after advance voting was blocked in several parts of the capital last Sunday. 

Around 130,000 police are set to protect 93,000 polling stations across the country.

Authorities said protesters were also blocking ballot boxes being delivered to polling stations across southern Thailand. 

Opposition protesters, mainly the Bangkok middle classes and southerners, backed by factions in the elite, are demanding Ms Yingluck's elected government step down.

They would like to see unelected "people's council" to oversee loosely defined reforms to tackle corruption and alleged vote-buying.

The backdrop to the protests is a years-long political struggle pitting the kingdom's royalist establishment.

The protests are backed by the courts and the military against Mr Thaksin, a billionaire tycoon-turned-politician.

Ms Yingluck is likely to win tomorrow's poll, helped by strong support in her brother's north and northeastern heartlands. 

But uncertainty hangs over the results, with unrest threatening polling and several constituencies without a candidate. 

Some 440,000 people prevented from casting ballots last week are due to vote on 23 February.