Tourists huddled in their hotel rooms and ducked inside buildings after bombs, one after another, exploded in at least four areas of Thailand, including popular beach cities, killing at least four people and wounding dozens more.

"The security in the bar told me to get back into the bar and they just shut down the shutters and made sure everyone was at the back of the bar and after about ... a 10 minute or so wait, there was a second bang," tourist Shane Brett told Australian Broadcasting Corp. from his hotel room in Hua Hin on Friday, the morning after the Thursday night blasts.

Those attacks killed a street vendor and wounded about 20 other people in the beach city about 200 kilometers (120 miles) southwest of Bangkok. Another pair of bombs exploded Friday morning in Hua Hin, killing one person and wounding four. Official with hospitals that treated victims of both blasts said they are from countries including Germany, Italy, Austria and the Netherlands.

Bombs also went off on Phuket's Patong Beach in southern Thailand and the southern provinces of Trang, Surat Thani and Phang Nga. One person was killed in the Trang blast, which occurred Thursday, and another was killed in the Surat Thani attack on Friday morning.

Police said it was too soon to say who was behind the attacks, but added that they had ruled out international terrorism.

Phuket in particular is frequented by millions of European, Chinese and Thai tourists each year who come to swim in the warm, azure sea, party at the open air night clubs and explore tropical rainforests. The other towns hit are less prominent international destinations but still popular among Thais and many foreigners.

Even as police searched for suspects and fears of more bombs continued, locals said the explosions will be a blow to tourism, a critical source of income. Governments including the U.S., Germany, Australia and Britain advised their citizens traveling in Thailand to take precautions.

Tourism suffered a temporary hit after a bomb blast ripped through a Bangkok shrine nearly a year ago, killing 20 people, mostly visitors from other Asian countries.

"This ruins business. Hotels, restaurants, tours, we were already suffering, but this, it's going to ruin our lives," said Hua Hin Adventure Tours guide Natsupa Dechapanya.

Natsupa raced Thursday from hotel to hotel visiting clients and warning them not to go outside, especially where people gather. She was also fielding cancellation calls, although she was staying away from her office, opposite a clock tower where Friday's bombs went off.

"I'm scared, it's bad," she said. "This is the first time this has happened in Hua Hin. We think of this as a safe town, but now everyone is fearful. We feel like we're not safe."

She said because the explosions happened hours apart, many — including herself — are worried about whether the attacks are over. And she said without any arrests, tension on city streets is palpable.

"Usually this is a friendly town, but today no one wants to look up. People don't want to look each other in the eyes," she said.

Thailand's economy has struggled since a 2014 military coup; investors grew wary and have stayed away, but tourists came back, even after last year's shrine bombing. More than 14 million people visited between January and May 2016 — up from 12.5 million the year before, according to the Tourism Authority of Thailand. Almost 4 million of this year's tourists came from China, just about 400,000 from the U.S.

Earlier attacks have been tied to political turmoil. Friday was a national holiday in Thailand marking the Queen's birthday, also Mother's Day. They came less than a week after voters approved a new, junta-backed constitution.

Sirasit Teimtontanin, a manager at City Beach Resort in Hua Hin, said one of Friday's explosions went off about 300 meters from the front door. The resort's 50 guests were asked to stay inside, but Sirasit said by late morning, some were venturing out to the beach on a balmy day. Stores, shopping malls and movie theaters were closed. But aside from heavy police presence, he said, his town seemed normal.

Nonetheless, he said he's very concerned about the impact of the bombings on tourism at Thailand's beach resorts. More than 15 rooms had been cancelled within hours Thursday.

"We've never had anything like this in our city," he said. "Thai tourists will understand the police have the situation under control, but I think European tourists might not be coming."

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Rod McGuirk contributed to this story from Canberra, Australia.

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Follow Martha Mendoza on Twitter: @mendozamartha