Better known for its white sands and smiles, Thai tourism is taking a battering as the latest gruesome protests in Bangkok have frightened off visitors to the kingdom.

Would-be tourists considering massage, temples and spicy food in the Thai capital this week may have been put off by scenes, televised worldwide, of red-clad protesters throwing bottles of their own blood at government offices.

The so-called Red Shirts, supporters of former prime minister Thaksin Shinawatra, are trying to force snap elections.

And although their rally has been peaceful so far, many recall the Red Shirts' protests last year that turned violent and came months after airport blockades by the rival Yellow Shirts that left tens of thousands of visitors stranded.

Thai travel agents' representative Surapol Sritrakul said the crimson protests had led to many tour cancellations, particularly in key Asian markets, estimating that tourism figures were down 20-30 percent on the yearly average.

"Blood is scary. Many people think the protests could be violent. They think the blood could come from killing. It's not a good image for Thailand," said Surapol, president of the Association of Thai Travel Agents.

Thailand's tourism authority said 38 countries had issued travel warnings for Bangkok over the rally that began last weekend.

But the Red Shirts' pouring of their own blood was only the latest, though most bizarre, piece of political theatre to be seen in Thailand since a military coup in 2006 that overthrew their hero Thaksin.