Thousands of Thai opposition protesters have marched on government buildings in the capital as part of their "shutdown" of Bangkok aimed at derailing elections and toppling the government.

Protesters have tried to block seven major intersections in Bangkok on Tuesday in an attempt to force the city to grind to a halt.

There have been at least eight deaths and around 500 people injured in connection with the political unrest.

Demonstrators stopped officials from going to work at several key ministries on Tuesday in an attempt to intensify pressure on Prime Minister Yingluck Shinawatra.

The protesters, led by a former opposition MP, want Yingluck to resign to make way for an unelected "people's council" that would oversee reforms to curb the political dominance of her billionaire family.

Their two-month rallies have pushed the government to call snap February 2 polls, but the protesters have rejected the vote in the latest twist of a political crisis that has gripped Thailand since Yingluck's brother Thaksin was ousted in a military coup seven years ago.

Several thousand demonstrators gathered outside the Thai customs department to prevent staff from going to work.

With protesters' plans to surround all government ministries and politicians' homes, many fear that Thailand is teetering on the brink of widespread violence.

"This is not democracy. It is autocracy... it is a one-man rule," said rally leader Satish Sehgal, railing at former Prime Minister Thaksin's alleged stranglehold on the nation's politics.

"There's massive, rampant corruption in this country. Nepotism. Our objective is to try and get rid of all this."

Demonstrators also surrounded the ministries of commerce, labour and information and communications technology.

Return to work

It is a tactic they have deployed several times during the months-long protests, which have so far failed in their goal of forcing Yingluck from office.

Many key junctions remained blocked in the Thai capital with loudspeakers broadcasting bombastic speeches into the city air after protesters launched the shutdown on Monday, causing widespread disruption to Bangkok's central retail and hotel districts.

But the number of demonstrators on the streets appeared to have declined as some returned to work.

The well-organised protest movement has vowed to occupy parts of the city of 12 million people until Yingluck quits, threatening to disrupt the February election which it fears will only return the Shinawatra clan to power.

A hardcore faction of the movement has threatened to besiege the stock exchange and even air traffic control if Yingluck does not step down within days.

Deputy Prime Minister Surapong Tovichakchaikul insisted that the government was still functioning.

He said the shutdown was expected to last about one week, urging protest leaders to join talks to find a way out of the crisis.

The government was assessing whether it was possible to delay the election under existing laws as proposed by the Election Commission, he added, explaining "the doors are not shut" on that option.

So far the shutdown itself has been peaceful, although eight people have been killed and hundreds injured in street violence in recent weeks.

The rallies were triggered by a failed amnesty bill that could have allowed Thaksin to return without going to jail for a past corruption conviction.

Source: Agencies