The blast occurred about 6:30 pm 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.
"The death toll is now 16," police spokesman Prawut Thavornsiri told AFP, adding the blast was likely politically motivated and designed to bring "chaos" in a the junta-ruled kingdom.
Glass was strewn across the street after the explosion outside the Erawan Shrine in the central Chidlom district, an AFP reporter witnessed.
Charred and shattered motorcycles littered the scene, along with hunks of concrete from the shrine, with pools of blood on the pavement and two bodies crumpled on the steps of the shrine.
"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.
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 an Kobkarn Wattanavrangkul told AFP as she visited the hospital.
A Chinese and a Filipino were among those confirmed dead, Thai police said.
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.
Meanwhile Reuters reported at least 27 people were killed including foreign tourists, in an attack the government said was a bid to destroy the economy.
There was no immediate claim of responsibility for the blast at the Erawan shrine at a major city-centre intersection.
"The perpetrators intended to destroy the economy and tourism, because the incident occurred in the heart of the tourism district," Defence Minister Prawit Wongsuwan told Reuters.
The government would set up a "war room" to coordinate the response to the blast, the Nation television channel quoted Prime Minister Prayuth Chan-ocha as saying.
Two people from China and one from the Philippines were among the dead, a tourist police officer said.
Domestic media said 27 people had been killed, 10 of them men and 17 women.
Police said 81 people were wounded. Media said most of them were from China and Taiwan.
The Erawan is an enormously popular shrine to the Hindu god Brahma but is visited by thousands of Buddhist devotees every day.
It is located on a main road through Bangkok's commercial hub and is surrounded by three major shopping malls.
Police and ambulances rushed to the scene after the bomb went off around 7pm (1200 GMT) local time.
Officials close off an intersection after an explosion in Bangkok, Monday, Aug. 17, 2015. - AP Photo/Sackchai Lalit
Meanwhile the Malaysian Embassy’s Security Liaison Officer in Bangkok, ACP Fauzi Khan Ismail told Astro AWANI the death toll from the incident is expected to rise as the area was a tourist hotspot.
He said, initials reports indicate the death toll could reach 15 dead while 70 others injured.
It is believed that only one from three bombs planted at the scene had exploded.
Police have also cordoned off a 500 square metre radius area around the incident.
Fauzi said, they have yet to confirm whether Malaysians were among the victims and that search and rescue efforts were still ongoing.
