BANGKOK (Reuters) - Police said on Monday the trail had gone cold in the hunt for a bomber a week after 20 people were killed in Thailand's worst ever bomb attack, and they were unsure if the chief suspect was still in the country.

Although half of the 14 foreigners killed in the blast at Bangkok's most famous Buddhist shrine were from mainland China or Hong Kong, tour operators said there was little sign that Chinese holidaymakers had been put off visiting Thailand, providing some relief for the economy, at least.

The main evidence police have to go on is security camera footage. Some, from the Erawan shrine, shows the suspected bomber slipping off a backpack and walking away.

The young man with a yellow shirt and dark hair was also caught on closed circuit television (CCTV) camera leaving the scene on the back of a motorcycle taxi. But after that there was very little, police said.

"In terms of the CCTV cameras, some don't capture images properly and some were damaged which is a waste of time for police piecing together where the suspect went," national police chief Somyot Poompanmuang told reporters.

In the days following the attack, authorities issued contradictory statements about the suspect's appearance, the number of accomplices he might have had and the likelihood of foreign involvement.

"You want the truth? We don't know if the suspect is still in Thailand but I have to assume he still is because we've got no information that he left," Somyot said.

The government said the bomb was aimed at undermining the economy by hurting tourism, an even more vital industry as growth flags in other sectors.

The military government wants growth as it steers the country towards an election next year under a new constitution critics say will not end a decade of turbulent politics.

The government has been trying to reassure tourists and foreign governments, and plain clothes police have fanned out across Bangkok, said police spokesman Prawut Thawornsiri.

The Thailand-China Tourism Association, which oversees more than 200 operators bringing Chinese visitors, said, however, the bomb had not scared people away. China is Thailand's biggest source of tourists.

"There have been maybe one or two cancellations here and there. Nothing major," association resident Ronnarong Cheewinsiriamnuai told Reuters.

Chinese operators have not canceled charter flights and overall, Ronnarong said, he had seen a dip of about 2 percent in Chinese visitors.

The junta said on Monday that according to its survey, "tourists are not too concerned", about the attack.