About 40,000 soldiers and police were mobilised in the capital from Friday, when several thousand red-shirted supporters of deposed premier Thaksin Shinawatra gathered at several points in “warm-up” events ahead of the main rally on Sunday.
Investors are worried about violence, and also about the government being distracted when it should be concentrating on nurturing the economy as it recovers from a brief recession.
But Thailand is still benefiting from investment funds flowing into Southeast Asia and foreigners have snapped up $500 million (329 million pounds) of Thai stocks so far this year, much of it this month.
The stock market rose 1 percent on Friday, turning round late in the session when the day’s protests were seen to have passed off peacefully.
The leaders of the “red shirts” say they will stay in Bangkok for at least seven days, aiming to force Prime Minister Abhisit Vejjajiva to call an election that Thaksin’s allies would be well placed to win.
“Some 600,000 to 700,000 ‘red shirts’ are on their way to Bangkok and, together with those already in town, we will have more than a million people,” Woravat Auapinyakul, a member of parliament for the pro-Thaksin Puea Thai Party, told reporters.
Many businesses and schools were shut in the capital on Friday and some companies allowed staff to work from home.
Armed guards stood at many banks and state buildings after government warnings of potential sabotage, including bombings.
Economists caution that possible unrest could hurt some businesses and sap consumer confidence in Southeast Asia’s second-biggest economy, possibly forcing the central bank to delay an expected rise in interest rates from record lows.
Most expect the rising trend in Thai stocks, among the cheapest in Asia, to remain intact, noting that violent protests in April 2009 failed to unseat the government.
The protests add a new chapter to a seemingly intractable political conflict pitting the military, the urban elite and royalists, who wear the revered king’s traditional colour of yellow at protests, against the mainly rural Thaksin supporters.
The protesters say the Oxford-educated Abhisit came to power illegitimately, heading a coalition cobbled together by the military after a pro-Thaksin party leading the previous coalition government was dissolved by the courts.
Thaksin was toppled in a military coup in 2006 and later sentenced in absentia to two years in prison for corruption.
The “red shirts” chafe at what they say is an “unelected elite” preventing allies of twice-elected Thaksin from returning to power through a vote. Adding to their anger, Thailand’s top court seized $1.4 billion of his assets last month, saying it was accrued through abuse of power.
Woravat said Thaksin was in Dubai, his base since he fled into exile to escape the graft sentence, but that he would be flying to Europe soon to meet up with his daughters. Media reported that he would see them in Germany.
Abhisit spent the night in a Bangkok military barracks, which is his centre of operations for the duration of the rally.
Few expect a million protesters in Bangkok this weekend, but the prospect of even tens of thousands flooding the streets has rattled nerves in the city of 15 million people.
Protesters accuse the authorities of trying to fan the fears with talk of possible bombings and arson, but the government insists the threat of violence is real.
Government House, which includes Abhisit’s office, has been cordoned off. The authorities have closed several other roads to prevent protesters from besieging government buildings.
In 2008, a rival protest group sought to topple a Thaksin-allied government by seizing Government House for three months and shutting Bangkok’s two main airports for eight days. The UDD insist they will not use the same tactics. Reuters