Nitithorn Lamlua, the leader of one group of protesters who have shut down parts of Bangkok, said protest leaders have already been charged with treason so they had nothing to lose.

“We will fight until we win,” he said.

Until now protest leaders have declared Thailand’s commercial hub and transport system, including the capital’s airports, off-limits as protesters have occupied  government ministries and  seized key intersections across the capital.

Transport Minister Chadchart Sittipunt urged protesters not to shut down the airport at the peak of the tourist season and to “think of the country”.

Ms Yingluck has invited leaders of anti-government protesters, political parties, the Election Commission and other state agencies to discuss delaying elections set for February 2.

But protest leader Suthep Thaugsuban turned down the offer, saying his movement would accept nothing less than the resignation of Ms Yingluck’s entire cabinet.

Bangkok’s The Nation newspaper quoted unnamed sources as saying Ms Yingluck had considered resignation last Sunday but changed her mind at the last minute after a telephone call from her elder brother Thaksin Shinawatra, who lives in self-imposed exile in Dubai. The report could not be verified.

Protesters accuse Mr Thaksin, a former prime minister ousted in a 2006 coup, of running the country from abroad, which Ms Yingluck denies.

The International Crisis Group, a Brussels-based research organisation, warns that the “scope for peaceful resolution is narrowing” in Thailand and that the campaign to stop elections “raises prospects of widespread political violence” and could provoke a military coup.

“Competing Thai elites – with mass backing – disagree fundamentally about how political power should be acquired and exercised,” the group said.

“There is no clear way out. But there are ways to render a bad situation potentially catastrophic.

“Denying the chance to vote is one. So is the propensity of some leaders to achieve by mass action – often violent – what they cannot by popular mandate or negotiation.”

Thousands of protesters camping near huge stages set up at Bangkok intersections say they are prepared to continue their protest for days.

The protest has crippled traffic flows across the city of 12 million.

Despite  the Australian government’s travel advisory recommending that Australians stay away from the protests, Melbourne tourists Steve Abbott and Paul Williamson joined whistle-blowing demonstrators outside the city’s Central World shopping mall, which was set alight during protests in 2010.

“Look at the crowd. You can pretty much tell they are a very normal sort of peace-loving community,” Mr Abbott told the Bangkok Post.

“It’s not like a bunch of rioters going crazy, as I think we would be at home,” he said. “If this was Singapore they would probably have the water cannons on them by now.”

Since the unrest broke out in November, eight people have been killed and hundreds injured.