Tourism is one of the few bright spots in an economy that continues to underperform more than a year after the military seized power in May 2014. The sector accounts for about 10 percent of the economy, and the government had expected a record number of visitors this year following a sharp fall in 2014 during months of street protests and the coup.
Thai national police spokesman Prawut Thavornsiri said on Tuesday the death toll stood at 22 from the bombing, with 123 people wounded.
Three Chinese were among the dead, the official Xinhua news agency in China said. Two Hong Kong residents, two people from Malaysia and one person from the Philippines had also been killed, officials said. Many of the wounded were from China and Taiwan, according to local media.
Police teams were deployed to the blood splattered site early on Tuesday, with some wearing white gloves and carrying plastic bags, searching for clues. "Collection of evidence last night was not complete," Udomdej said.
The shrine, on a busy corner near top hotels, shopping centers, offices and a hospital, is a major attraction, especially for visitors from East Asia, including China. Many Thais also worship there.
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"It was like a meat market," said Marko Cunningham, a New Zealand paramedic working with a Bangkok ambulance service, who said the blast had left a two-meter-wide (6-foot-) crater.
"There were bodies everywhere. Some were shredded. There were legs where heads were supposed to be. It was horrific," Cunningham said, adding that people several hundred metres away had been injured.
At the scene lay burnt out motorcycles, with rubble from the shrine's wall and pools of blood on the street.
Earlier, authorities had ordered onlookers back, saying they were checking for a second bomb but police later said no other explosive devices were found.
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Authorities stepped up security checks at some major city intersections and in tourist areas. The city's elevated railway, which passes over the scene, was operating normally.
While initial suspicion might fall on Muslim separatists in the south, Thailand has been riven for a decade by an intense and sometimes violent struggle for power between political factions in Bangkok.
Occasional small blasts have been blamed on one side or the other. Two pipe bombs exploded outside a luxury shopping mall in the same area in February, but caused little damage.
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In Washington, the U.S. State Department said it was too soon to tell if a blast was a terrorist attack. Spokesman John Kirby said authorities in Thailand were investigating and had not requested U.S. help so far.
He said U.S. officials were working with Thai authorities to determine if any U.S. citizens were affected by the blast.
The shrine intersection was the site of months of anti-government protests in 2010 by supporters of ousted former Prime Minister Thaksin Shinawatra. Dozens were killed in a military crackdown and a shopping center was set ablaze.