Huge crowds of Thai opposition protesters occupied major streets in central Bangkok on Monday in an attempted "shutdown" of the capital, escalating a campaign to unseat the embattled premier.

The demonstrators want Prime Minister Yingluck Shinawatra to resign to make way for an unelected "people's council" that would oversee reforms to curb the political dominance of her billionaire family and tackle a wider culture of money politics.

Tens or even hundreds of thousands of flag-waving protesters massed at key intersections in the city, setting up rally stages along with tents for sleeping and stalls offering free food.

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

In the eyes of the protesters, Yingluck is "no longer prime minister", firebrand protest leader Suthep Thaugsuban told reporters while leading a march through the capital.

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

The government said it would invite all sides to a meeting on Wednesday to discuss the election commission's proposal to postpone the February 2 election, although it looks unlikely to agree to the demonstrators' demand for a delay of at least a year.

The International Crisis Group think-tank warned Monday of a "potentially catastrophic" situation if people are denied the chance to vote.

"As anti-government protesters intensify actions, the risk of violence across wide swathes of the country is growing and significant," it said in a report.

Disruption but not total shutdown

Within hours of launching the shutdown, the movement succeeded in bringing widespread disruption to Bangkok's central retail and hotel districts, large swathes of which were taken over by whistle-blowing demonstrators.

Many schools were closed and some residents stockpiled food and water, but the city of roughly 12 million people -- which has grown accustomed to large political rallies in recent years -- did not grind to a complete halt.

The city's subway and skytrain were running as usual, shops and restaurants were open and demonstrators promised to leave a lane unblocked at each major intersection to allow ambulances and buses to pass.

While there was the usual Thai carnival atmosphere, protests in the kingdom have a history of suddenly turning bloody, often at night and sometimes involving unidentified gunmen seeking to incite violence.

Eight people, including a policeman, have been killed and dozens injured in street violence since the protests began over two months ago.

Fanning tensions, several shots were fired in a drive-by shooting at the headquarters of the opposition Democrat Party early Monday, while elsewhere a protest security guard was shot and wounded in a quarrel, police said.

Ongoing political crisis

The protests are the latest chapter in a years-old political crisis that has gripped Thailand since Yingluck's older brother, fugitive former premier Thaksin Shinawatra, was ousted by royalist generals in 2006.

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

The billionaire tycoon-turned-politician has strong electoral support in northern Thailand, but he is reviled by many southerners, Bangkok's middle class and members of the royalist establishment.

Roughly 20,000 police and soldiers were due to be deployed for the shutdown, although there was little sign of them on the streets.

The government has not tried to stop the protests, despite warnings that they could take a heavy toll on the economy and local businesses if they drag on.

"Of course it affects me -- I'm very stressed," said hair salon owner Tong, 69. "No customers are coming now as my regular customers cannot drive here."

Smaller rallies have been held in the capital to back the February election and oppose the shutdown, while thousands of government supporters gathered in various cities in northern Thailand.

The civil strife is the worst since 2010, when more than 90 people were killed in street clashes between pro-Thaksin protesters and armed soldiers.

The military -- traditionally a staunch supporter of the anti-Thaksin royalist establishment -- has said it will not crack down on the latest protests, which come as the country quietly braces for the end of ailing King Bhumibol Adulyadej's more than six-decade reign.