Thai police said Tuesday they are hunting for a suspect seen in CCTV footage who they believe may be connected to the bombing, which ripped through crowds gathered near the Erawan Shrine on Monday evening, killing at least 22 people and reportedly injuring about 120.
In one CCTV image released by police, the man is seen carrying a dark-colored backpack near the shrine. In another, he no longer has the backpack. He's wearing a yellow T-shirt and dark-framed glasses.
Royal Thai Police Commissioner Gen. Somyot Poompanmoung said authorities don't yet know the suspect's identity or whether he is Thai or a foreigner.
"We need more evidence before we can make any conclusions," he told reporters at a news conference, saying that police were studying more than 10 days' worth of CCTV footage from the area.
The shrine, situated at a bustling intersection near a large shopping mall, is a big draw for tourists. At least seven people from other Asian countries were reported to be among the dead as well as one Briton. The site is popular among Buddhists as well as Hindu and Sikh members of Thailand's Indian community.
"From this incident, it is apparent that there are active individuals or groups that harbor the intention to damage Thailand, who may be pursuing political gain or other intentions by damaging the economy and tourism," Prime Minister Prayuth Chan-ocha said.
Adding to the jitters, a new explosion was heard Tuesday at a pier on the Chao Phraya River that flows through Bangkok, police told CNN. No injuries have been reported, and the pier has been closed, said police spokesman Lt. Gen. Prawut Thavornsiri.
It was unclear whether the two blasts were connected in any way.
The first explosion struck at about 7 p.m. Monday during a busy time in the area, sending a giant plume of smoke and flames into the air.
"It was like this huge gust of wind and debris flying through you," recalled Sanjeev Vyas, a DJ from Mumbai, India, who was in the middle of the fray. "And then I see bodies everywhere; there are cars on fire, there are bikes everywhere. People are screaming."
Marko Cunningham, a paramedic who arrived soon after the explosion, described the scene as "absolutely horrific."
"I've seen a lot, but I've never seen injuries as vicious as these injuries," he told CNN, adding that "so many bones were broken."
Motorbike taxi driver Theerasak Kultham, 20, was among the injured. He told CNN he was stopped at a red light while taking a customer to a mall when suddenly he heard a loud explosion.
"I turned back to look at where the sound came from and saw people scattered on the streets everywhere. I decided to abandon my bike and ran off ... to the other side," he said.
He saw his customer's arm was covered in blood and realized his own back was numb and bleeding. Doctors said he had two shrapnel injuries -- and one piece may have to work its own way out.
"I've never been through (anything) like this before. I'm still scared," said Theerasak, who moved to the capital from a rural area to find work.
There has been no claim of responsibility for the attack. Thai authorities haven't made any announcements about who they believe might be behind it.
Somyot, the police commissioner, said cryptically on state-run TV that authorities had been warned about possible attacks, but they didn't know where or when they might occur.
Analysts say it's unclear which group would want to carry out the shrine attack, which is likely to hurt Thailand's tourism industry, a key part of the economy.
The capital, which was convulsed by political unrest last year, has experienced small-scale bomb and grenade attacks in the past. Two devices exploded at an upscale shopping mall in February but didn't cause any casualties.
But Monday's attack was of a different magnitude.
"It is by far the most devastating attack that Bangkok has seen -- or Thailand has seen, for that matter -- as far as I can remember," said Joseph Liow, a senior fellow at the Brookings Center for East Asia Policy Studies.
"CITY BOMB HORROR" blared a Tuesday headline in the Bangkok Post.
Observers say the attack doesn't fit with the campaign of violence mounted by Islamic insurgents in the far south of Thailand, near the border with Malaysia.
"Their complaints are very local, and they have tended to attack military and security targets," said CNN global affairs analyst Bobby Ghosh. "They have not really committed a terrorist attack of this nature against civilians, much less tourists. This does not seem to bear their fingerprints."
Experts say the shrine attack could be linked to the political instability that has plagued Thailand in recent years.
The military seized power in a coup in May 2014, ousting the democratically elected government that had been beset by long-running protests in Bangkok.
"There are political groups that are opposed to military rule, but they're democrats and this is not their style either," Ghosh said. "They don't go around bombing innocent civilians. And hurting Thailand's economy, which this will do, is the last thing that they would want."
Cunningham, the paramedic who witnessed the aftermath of Monday's attack, said the bomb was "obviously designed to cause maximum damage and death" and was "really unlike the bombs that the Thailand political groups use."
Thai state media cited Somyot, the police chief, as saying the device that exploded was a pipe bomb wrapped in white cloth.
But CNN intelligence and security analyst Bob Baer expressed skepticism.
"With that much damage, that many deaths, it's very unusual," he said. "It would be a very sophisticated pipe bomb -- they don't usually kill that many people."
Authorities were still identifying the attack's victims Tuesday.
UK Foreign Secretary Philip Hammond said a British woman living in Hong Kong was among those killed, and condemned what he called "a callous act of violence against completely innocent and unsuspecting members of the public."
Prime Minister David Cameron said via Twitter he was deeply saddened by the news.
Five Thais, four Chinese, two Malaysians and a Singaporean are also among the dead, said Maj. Gen. Witoon Nitiwarangkul, the surgeon general at Bangkok's Police General Hospital.
Singapore's Foreign Ministry confirmed the death of a young Singaporean woman and said seven other Singaporeans were wounded.
A ministry spokesman extended the country's deepest condolences to the woman's family, saying a "life of promise" had been "snatched away in a moment of terror."
Medical officials had earlier reported that a Filipino was killed in the attack, but the Philippine Department of Foreign Affairs said it was still verifying that claim, according to the state-run Philippines News Agency.