Thailand's flood crisis is taking its toll on the kingdom's lucrative tourism sector, scaring off nervous holiday-makers even though the most popular destinations remain unscathed.

Since deadly monsoon rains began three months ago, images of inundated Thai homes and frightened residents wading through water have appeared worldwide and dented the allure of the "Land of Smiles", typically associated with sunshine.

Many would-be tourists are now putting off their visits to the kingdom, according to industry groups, in another major blow little more than a year after the capital was rocked by two months of deadly political unrest.

The Association of Thai Travel Agents (ATTA) reported new bookings have fallen by up to 70 percent compared to usual levels for the month, while Tourism Authority of Thailand deputy chief Sansern Ngaorungsi said cancellation rates had reached about 25 percent.

"More and more cancellations are coming," he told AFP.

The floods have killed more than 300 people and affected millions of Thais mostly in the north and centre, but the main tourist attractions -- including the southern islands of Samui, Phuket and Phi Phi -- are so far unaffected.

Fears are now growing for the low-lying capital Bangkok, home to 12 million people and a regional transit hub, after the government admitted it was failing in its battle to hold back huge floods just north of the city.

Singapore has warned its nationals against all but essential travel to the capital, while tour operators in China said visitors to Thailand had dropped dramatically as they advised against holidays in the troubled kingdom.

"Nobody wants to come to Bangkok," said the marketing manager of a luxury riverside hotel in the city, asking not to be named.

While its elevated parking lots were packed with the Ferraris and sports cars of Thai residents attempting to keep their prized vehicles dry, the hotel was struggling to fill up its rooms.

"We are flooded by cancellations," said the manager, adding that the company chain -- with fewer than 20 hotels nationwide -- had already lost more than half a million US dollars through cancelled bookings, most of them corporate.

Others were more confident that Bangkok could escape the worst of the crisis.

"What we are trying to tell guests is that the city is not really affected," said Annabelle Daokaew, PR manager at the Four Seasons Hotel in the upmarket commercial district, where the occupancy rate remained at more than 80 percent.

"We can't blame them if they are worried."

Tourists shopping in the capital were undeterred by the prospect of swapping sandals for rubber boots, but were still taking precautions.

Chris Robson, a 53-year-old from Brisbane in Australia, had moved from a central hotel to one nearer the airport.

"It feels safer back out there," she said. "But it's a hassle to come in to town."

New arrivals seemed unsure of what to expect as they touched down at the city's main airport, Suvarnabhumi, which is still operating as normal with reinforced flood defences at a height of up to 3.5 metres.

"I'm just relying on a local friend who told me it's safe to go to Bangkok. There isn't really much information. I've no idea how bad it is," said Marjolijn Salverda, 27, from Holland, as she waited to collect her luggage.

Protecting the massive air hub, built on a drained marsh, has been a priority for the Thai authorities, aware of the crippling effect that its closure could have on the country's economy.

In 2008 a nine-day blockade by political protesters stranded tens of thousands of travellers and badly damaging Thailand's tourist-friendly image.

The industry was badly hit again last year, when Bangkok's central shopping area was reduced to a battle zone during an army crackdown on mass demonstrations by anti-government "Red Shirt" protesters.

Tourism leaders were hopeful that businesses would once again bounce back from the natural disaster now befalling the country.

"I think if we can protect the airport, then bookings can be expected to recover after the floods recede," said Association of Thai Travel Agents vice president Chidchai Sakornbadee.

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