By Pracha Hariraksapitak and Kitiphong Thaicharoen
BANGKOK (Reuters) - Hundreds of protesters stormed the grounds of Thailand's parliament on Wednesday, forcing government ministers to flee by helicopter and raising pressure in a four-week street rally seeking snap elections.
The red-shirted supporters of ousted premier Thaksin Shinawatra later retreated, but tens of thousands remain in Bangkok's main shopping district, refusing orders to leave until Prime Minister Abhisit Vejjajiva dissolves parliament.
The scene outside parliament was among the most chaotic and confrontational since the sporadic protests began on March 12.
Protesters massing outside gates of the sprawling complex pressed up against a line of police in full riot gear. When some "red shirts" forced open the iron gate, police melted away and hundreds swarmed onto the grounds, including dozens packed on the back of a truck that drove into the main entrance.
They pressed up against security forces outside the lobby doors but left after about 20 minutes only to gather again outside the gates, brandishing guns and tear-gas canisters they said were seized in a scuffle with military police.
"We have achieved our mission today," Korkaew Pikulthong, a "red shirt" leader, told the crowd through a bullhorn.
Ministers had held a cabinet meeting inside the building earlier but some had left before the protesters broke through. Deputy Prime Minister Suthep Thaugsuban and several other ministers escaped by helicopter.
"Many of us climbed over a parliament wall to an adjacent compound where a government helicopter waited to take us away," Satit Wongnongtoey, a minister attached to the prime minister's office, said on television.
MARKETS FIRM DESPITE TENSION
Despite the tension, Thai stocks and the baht currency rose on confidence the government, with its support from the military and the royalist establishment, will survive the increasingly bold showdown with the mostly rural and working class protesters.
Finance Minister Korn Chatikavanij, however, said prolonged protests could inflict damage on the economy, Southeast Asia's second biggest, by causing output this year to be "significantly worse" than a government projection of 4.5 percent growth, and possibly delay an expected interest rate rise.
Another month of protests, he said, "... would be intolerable, not only to the economy as a whole but for the sanity of Bangkokians."
Most economists expect Thailand' benchmark interest rate to rise in June from a record low of 1.25 percent.
The government extended a tough Internal Security Act that allows troops to impose order, but there was no sign of an imminent crackdown. The army, which is central in the balance of power, is refusing to use force to disperse the crowd.
Army chief Anupong Paojinda said there was no justification to move in despite pressure from Abhisit to impose the law, an unidentified source told the Bangkok Post newspaper.
"We can't since it will cause losses," the source quoted Anupong as telling Abhisit. "They all are Thais."
Foreign investors have been ploughing money into the fast-recovering economies of Southeast Asia and have not left Thailand out despite the turbulence. Since February 22 foreigners have bought a net $1.73 billion of Thai stocks.
Thai stocks, which have risen more than 80 percent over the past 12 months, were up 1.1 percent at the midsession break, just after the incident at parliament.
There is concern, however, the crisis could squeeze longer-term foreign direct investment, or FDI, which was has been volatile since a 2006 military coup ousted the twice-elected Thaksin after allegations of corruption and nepotism.
"I've been getting a sense for the first time in the more than three years since the coup that FDI -- including our client base -- is really taking a hard look at Thailand long-term because of this," said Roberto Herrera-Lim, an analyst at Eurasia Group, a consultancy.
Abhisit is facing pressure from Bangkok's elite and middle class and even his own government to halt the rally, but has held back to avert a confrontation many believe would cause even greater damage. Threats to arrest the protesters have not been carried out, emboldening the movement.
The "red shirts" have taken aim at the urbane, Oxford- and Eton-educated economist, whom they see as a front man for an unelected elite and military that is secretly intervening in politics and operating with impunity.
They say Abhisit, who came to power in a 2008 parliamentary vote after courts dissolved a pro-Thaksin ruling party, should call an election and let the people choose their government. "Red shirt" leaders say they will respect the result.
(Additional reporting by Martin Petty; Writing by Jason Szep; Editing by Alan Raybould)
