On what should be a bonanza long weekend for the tourist industry in a seaside playground favoured by Thailand's royal family, shops and restaurants are shuttered, streets are empty and security forces are advising people to stay in their hotels.

The resort of Hua Hin was rocked by four bombs less than 12 hours apart that killed two people and wounded 24, as thousands flocked to its hotels and beaches for a long weekend to celebrate the Queen's birthday, which is also Mother's Day in Thailand.

"It's a ghost town now," said Irish tourist Tim Kelleher. "Usually this place is so popular."

The bombings were part of a series of attacks on world-renowned seaside resorts in southern Thailand that may jeopardise the Southeast Asian nation's target of luring a record 32 million visitors in 2016.

Tourism is one of the only growth sectors in Thailand, and accounts for 10 percent of an economy that has struggled under the stewardship of a military government that seized power two years ago.

"It's bad for the economy, which is limping along on one leg, and now we have these incidents," Ittirit Kinglek, the president of the Tourism Council of Thailand, told Reuters.

"It will definitely have an impact on tourism, but it's too early to estimate how it will affect tourist numbers and revenues."

Other blasts hit the island of Phuket, a resort town in Phang Nga province, and Surat Thani, the jumping off point for travellers heading to the white sandy beaches of Gulf of Thailand islands such as Koh Samui.

No group has claimed responsibility, though suspicion could fall on insurgents from Muslim-majority provinces in southern Thailand. Police and security analysts said the small devices appeared to be aimed more at sending a message than causing widespread death and destruction.

Embassies in Thailand warned their citizens to stay vigilant on Friday and some warned that there could be more attacks.

Australia, the source of just over 800,000 visitors to Thailand in 2015, issued a travel advisory saying Australians should "exercise a high degree of caution", and warned that "further explosions in any part of Thailand are possible."

China, the single biggest source of tourists to Thailand with nearly 8 million visitors in 2015, told citizens to avoid crowded areas and pay close attention to security developments.

FREE REFUND

The German units of tour operators TUI and Thomas Cook said customers booked on trips to Thailand departing before Aug. 15 could cancel or rebook to other destinations free of charge.

TUI, which has about 2,000 customers in Thailand at present, said it would help any who wished to leave early.

Thai Tourism Minister Kobkarn Wattanavrangkul said the sector was resilient and would rebound from any impact fast, as it had in the past.

"If anything happens, Thailand's tourism will be able to adjust and come back quickly," she told Reuters.

The attacks are the latest challenge to an industry that has weathered more than a decade of political instability and bounced back from several major setbacks in the past two years.

A bomb attack at a Hindu shrine nestled among luxury shopping malls and hotels in central Bangkok killed 20 and injured more than 120 in August 2015.

Tourist arrivals dropped by more than half a million in the month after the blast, but Thailand still hosted a record 29.88 million visitors in 2015.

A year earlier, months of sometimes deadly street protests paralysed the Thai capital before a coup in May 2014. The month after the military takeover, tourist numbers slipped to their lowest in more than two and a half years.

The attacks would hurt business and consumer confidence, Thai Airways Chief Financial Officer Narongchai Wongthanavimok told Reuters.

"To some extent, it should affect the Thai tourist industry and Thai Airways because confidence may be hit," he said. "But how much the impact will be, we need to monitor and assess the situation."

Business at budget airline Thai AirAsia was so far unaffected, Chief Executive Tassapon Bijleveld told Reuters.

Thailand's Erawan Hotel Group, one of the top five Thai hotel operators with a portfolio that includes two of the targeted resorts - Hua Hin and Phuket - has increased security at its hotels but not yet seen cancellations because of the blasts, group president Kamonwan Wipulakorn told Reuters.

At the Erawan shrine in Bangkok on Friday, the location of the 2015 bombing, there were no security checks as tourists and Thais visited, a Reuters witness said.

Australian tourist Vanessa Jamieson, at the shrine with 6-year-old twins on Friday, said the bombings in southern Thailand had made her rethink her holiday plans.

"We stayed away from most public places today," she said "Frankly, if the bombings continue then we might as well jump on a plane and go somewhere else." – Reuters