THEY came to bring down a government, risking attack by armed security forces. But there is a carnival atmosphere among more than 4000 protesters who have taken over the new $4 billion international airport in Bangkok, stranding an estimated 100,000 tourists and crippling the Thai economy.

No passport is required to pass through a checkpoint manned by "security guards", just a symbolic yellow scarf, the colour symbolising support for Thailand's King Bhumibol Adulyadej, and a clapper stick, which is to be clapped frequently.

No need to bring anything, except a mat to sleep on.

Woman serve hot noodles and sandwiches. Teenagers hand out ice-cream. Bottles of water are stacked metres high. Dozens of vehicles arrive throughout the day with boxes of food and supplies including toilet paper. Volunteer cleaners sweep the floors and neatly put rubbish in plastic bags.

Protesters can choose to rest on the road outside the main departure terminal, where speeches are made and musicians entertain on the back of a truck. Or they can spread out in the air-conditioned comfort of the terminal, listening to soft music playing over the speaker system or watching televisions tuned to local channels. The terminal's glossy shops are closed but undisturbed.

There are elderly couples, middle-aged women, teenagers and children. Some have brought their dogs.

The cars blocking access roads to the airport include Mercedes and BMWs, reflecting the support the protesters have among Bangkok's affluent middle class and elite.

But among the protesters are also grim-faced men carrying sharpened metal sticks and batons, some of them masked. These are the security guards who have shown they are not afraid to confront the Thai security forces.

"We want the police to come. We want to fight," one of the guards said.

When police tried on Saturday to block the roads and freeways to the airport a group of security guards chased them away after an angry confrontation. The police barricaded themselves in a nearby police station.

The overwhelming belief of protesters is that Mr Thaksin wants to turn the country into a republic, a threat to the 80 year-old monarch.

Inside the terminal Kriengsak Liew, 50, four other doctors and 20 nurses have set up a clinic stocked with medicines and a make-shift operating table.

Asked whether he was worried about an attack by security forces, Dr Kriengsak said: "No, we are not worried. If they come we have a plan to run inside, shut the doors and block the elevators … They will not be able to remove us, and the terminal will be destroyed."