The blast occurred on Monday in one of the Thai capital's most popular tourism hubs, ripping through a crowd of worshippers at the Hindu shrine close to five-star hotels and upscale shopping malls.
Chinese, Hong Kong, Singaporean, Indonesian and Malaysian citizens were among the 20 people killed, police said.
More than 100 other people were injured as the blast left body parts strewn across crushed pavement, alongside shattered windows and incinerated motorcycles.
Junta chief Prayut Chan-O-Cha on Tuesday branded the bombing the "worst ever attack" on Thailand, as he said the hunt was on for a suspicious man filmed on closed circuit television near the shrine.
"Today there is a suspect... we are looking for this guy," Prayut told reporters.
Police released CCTV footage showing the apparently young man in a yellow T-shirt walking near the shrine wearing a backpack, but then a short time later walking away without it.
"Things are becoming clearer now," Defence Minisiter Prawit Wongsuwon told reporters, although he declined to give details and authorities did not reveal if they had any motives for the attack.
Bangkok has endured a decade of deadly political violence amid a power struggle between the military, backed by the middle class and elite, and the poor led by populist politician Thaksin Shinawatra.
He is living in self-imposed exile after being ousted as premier in 2006. The junta has ruled the nation since May last year after toppling the elected government of Thaksin's sister, Yingluck.
Bangkok's power struggle has seen repeated rounds of deadly street protests and bombings for nearly a decade.
More than 90 people were killed in 2010 during clashes between security forces and Thaksin supporters -- many in the same area as Monday's bomb.
But the anti-junta groups have never conducted such a large attack, nor one that was apparently aimed at a tourist zone.
No obvious culprit
And with no-one claiming responsibility for Monday's assault, political and security experts said there was no obvious culprit.
Zachary Abuza, an independent expert on Thai security, told AFP he doubted it was in the interests of the anti-junta groups to carry out such an attack.
"Even if they are hell-bent on bringing down the government I just can't see them targeting a Hindu or any other religious shrine," Zachary Abuza, an independent expert on Thai security, told AFP.
"That would really alienate many of their supporters."
Muslim rebels from the country's far south have also waged a separatist insurgency for more than a decade that has claimed thousands of lives, mostly civilians.
But they have never been known to carry out substantial attacks in Bangkok, and Abuza as well as other analysts said Monday's bombing did not follow the insurgents' typical modus operandi.
Paul Chambers, director of research at the Institute of South East Asian Affairs in Thailand, said groups with links to military factions also had to be considered as potential suspects.
Various Islamic militant groups have also carried out many attacks in other parts of Southeast Asia, including on Indonesia's holiday island of Bali in 2002 that killed 202 people.
But they have not made Thailand a prime target.
Tourists 'targeted'
Junta leaders said the bomb was obviously aimed at damaging the country's tourist industry, which is a rare bright spot in an otherwise gloomy economy, and tarnishing the junta's reputation.
"(The attackers) had the clear target of destroying our economy and tourism.... and discrediting the government," Wongsuwon, the defence minister, told reporters.
Thailand's baht currency slumped to a more than six-year low on Tuesday and shares fell in Bangkok over concerns the attack could damage the tourism sector.
Built in 1956, the Erawan is an enormously popular shrine to the Hindu god Brahma but is visited by thousands of Buddhist devotees every day.
The bomb was detonated shortly before 7:00 pm (1200 GMT) in the middle of the city's rush hour, sending a fireball into the sky as commuters and tourists fled in panic.
Thais walking near the blast site on Tuesday expressed fear about more potential violence in the coming days.
"I'm worried about Bangkok, I don't know what will happen next," one woman, who gave her name as Rivewan, told AFP.
Adding to the tensions, a small explosion struck near a busy Bangkok train station on Tuesday afternoon, but police said nobody was injured.
Around 1,000 people queued for hours at a blood donation centre near the blast site on Tuesday, many crying as they waited to be seen by nurses.
"This shouldn't have happened to the Thai people," Pongchai Kulsitthiwong, a 45-year-old mobile phone seller told AFP, tears rolling down his cheeks while waiting to give blood.
Monday's attack drew quick expressions of grief from around the world. The US government released a statement warning its citizens to avoid the area, while also voicing sympathy for the victims. —Agence France-Presse
source: gmanetwork.com
