The blast occurred about 6:30pm (1130 GMT) when the streetside shrine was packed with worshippers and tourists – with the Thai police chief confirming at least 10 Thais, one Chinese and one Filipino citizen were among the dead.
“It was a bomb, I think it was inside a motorcycle… it was very big, look at the bodies,” one visibly shocked rescue volunteer, who did not want to be named, told AFP outside the Erawan Shrine.
Bangkok has endured years of deadly political violence, with a military junta now ruling the nation, and a decades-long Muslim insurgency in the far south that has claimed thousands of lives.
Police spokesman Prawut Thavornsiri told AFP the blast was likely politically motivated and designed to bring “chaos”, adding 16 people had been confirmed killed.
However no-one claimed responsibility for Monday’s attack, and it was unclear immediately who may have been responsible.
A spokesman for the government later said it was too early to speculate on who was behind the attack.
Islamic militants have 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.
Glass was strewn across the street after the explosion inside the gates to the shrine, which is in the central Chidlom district popular with tourists, an AFP reporter witnessed.
Charred and shattered motorcycles littered the scene, along with hunks of concrete, with pools of blood on the pavement and two bodies crumpled on the steps of the shrine.
The city’s medical emergency centre said more than 80 people were wounded by the blast, which rattled windows several kilometres from the site.
There were chaotic scenes at Chulakongkorn Hospital, one of a number of nearby medical facilities that received victims as nurses ferried the injured on gurneys.
One man who was conscious had visibly burned hair and a number of cuts that were bandaged, an AFP reporter on the scene said.
“Some (of the victims) are Chinese,” Minister for Tourism Kobkarn Wattanavrangkul told AFP as she visited the hospital.
A Chinese and a Filipino were among those confirmed dead, Thai police said, while Singapore’s prime minister said some of the city-state’s nationals were also wounded.
With rumours abounding in a city that is no stranger to major acts of violence, officials denied reports of more devices in an area, which is home to several high end hotels and major shopping malls.