BANGKOK, THAILAND- Thai protesters on Wednesday tightened their hold on Bangkok airport, where two people were wounded in a blast and thousands of travellers left stranded by demonstrators vowing to topple the government.

Two grenade attacks elsewhere in the capital deepened the sense of lawlessness after demonstrators stormed the airport Tuesday night, dramatically stepping up their campaign against Prime Minister Somchai Wongsawat. Suvarnabhumi Airport, a major Southeast Asian hub for millions of passengers, was closed down as guards from the People's Alliance for Democracy (PAD) protest movement sealed off roads to the facility.

"I have been informed by Thai Airways that 3,000 passengers are stranded at the terminal now," airport director Saereerat Prasutanont told AFP, adding that 78 outbound and incoming flights were affected.

Police said 8,000 demonstrators, most wearing yellow clothes in a traditional symbol of loyalty to the revered monarchy, had camped out at the three-billion-dollar airport overnight.

Another 1,500 were moving towards the terminal from Government House, the prime minister's office in central Bangkok which demonstrators have occupied since August, paralysing the government.

"It's not fair," said Vanessa Sloan, 31, from Florida, who arrived at the airport on Tuesday night and was supposed to fly on to the northern city of Chiang Mai on Wednesday.

"We spent the night here after all the check-in staff ran away," she said.

"No one is here to help."

Dejected passengers were camping out near the check-in desks surrounded by trolleys piled high with baggage, an AFP correspondent said. Some protesters were also sleeping in the terminal.

The taxi-drop off area outside the airport, which opened to great fanfare in 2006, had been turned into a huge stage where thousands of PAD supporters cheered speeches by their leaders.

The PAD - a loose coalition comprising royalists, Bangkok's old elite and the middle class - is spreading chaos ahead of the prime minister's return from a foreign trip later Wednesday.

The alliance accuses Somchai's government of being a corrupt puppet of exiled former premier Thaksin Shinawatra. Thaksin, who is Somchai's brother-in-law, was ousted in a 2006 coup.

Riot police have largely refused to tackle protesters amid fears of a repeat of clashes between protesters and police on October 7 that left two people dead and nearly 500 injured, the worst political violence in Thailand for 16 years.

Thailand's deputy premier said on Tuesday the government was ready to ask the military for help, but urged calm in the kingdom amid the spiralling situation.

Local television stations said a grenade was fired at protesters at Suvarnabhumi early Wednesday and emergency services official Petpong Kamchornkitkarn told AFP that at least two people were wounded.

A near simultaneous grenade attack on anti-government demonstrators picketing Bangkok's old Don Mueang airport, where Somchai has set up temporary offices, also wounded two people, Petpong said.

Another three were hurt when two grenades were tossed into a crowd of pro-government supporters on a road to Don Mueang, the site of a clash between rival activists that left 11 hurt on Tuesday, police said.

Somchai has rejected calls to quit. His plane back from the APEC summit in Peru was due to land at an undisclosed location on Wednesday evening. The PAD called this week's rallies in response to a grenade attack on Thursday that killed one protester. It launched the present campaign in May to emulate one in 2006 that led to Thaksin's downfall.