Thai authorities said on Tuesday they were looking for a suspect seen on closed-circuit television (CCTV) footage near a popular shrine where a bomb blast killed 22 people, including nine foreigners from several Asian countries.

The government said the attack during the Monday evening rush hour, in the capital's bustling commercial hub, was aimed at destroying the economy. No one has claimed responsibility.

Raising tension in the city on Tuesday, a small explosive was thrown from a bridge over a river but no one was injured, a police officer at the scene said.

National police chief Somyot Pumpanmuang said the suspect, who was wearing a yellow shirt and was seen in a first CCTV image with a backpack and then in a later one without the bag, could be Thai or a foreigner.

"That man was carrying a backpack and walked past the scene at the time of the incident. But we need to look at the before and after CCTV footage to see if there is a link," Somyot told a news conference.

Police earlier said they had not ruled out any group, including elements opposed to the military government, for the bombing at the Erawan shrine on Monday evening, although officials said the attack did not match the tactics of Muslim insurgents in the south.

Prime Minister Prayuth Chan-ocha also referred to the man as a suspect without giving details. He said there were "still anti-government groups out there", although he did not elaborate.

Police were deployed to the blood-splattered site on Tuesday, some wearing white gloves and carrying plastic bags, searching for clues to an attack that could dent tourism and investor confidence.

The Thai baht THB=TH fell 0.57 percent to 35.57 baht, its weakest in more than six years, on concern the bombing may scare off visitors. Thai stocks .SETI fell as much as 3 percent.

Police said the death toll was 22, with 123 people wounded. They said the blast was caused by a pipe bomb.

"Police are not ruling out anything including (Thai) politics and the conflict of ethnic Uighurs who, before this, Thailand sent back to China," Somyot said.

Thailand forcibly returned 109 Uighurs to China last month.

Hundreds, possibly thousands, of the Turkic-speaking and largely Muslim minority have fled unrest in China's western Xinjiang region, where hundreds of people have been killed, prompting a crackdown by Chinese authorities. Many Uighurs have traveled through Southeast Asia to Turkey.

The blast comes at a sensitive time for Thailand, which has been riven for a decade by a sometimes violent struggle for power between political factions in Bangkok.

An interim parliament hand-picked by a junta that seized power in a 2014 coup is due to vote on a draft constitution next month.