Bomb squad experts are sifting through the debris of a blast at a Bangkok religious shrine where at least 20 people were killed and scores wounded in an unprecedented attack on the city.
The hunt intensified for the bombers as shocked Thais struggled to come to terms with the scale of the carnage, which struck at dusk as worshippers and tourists thronged the streetside Erawan Shrine in the city's commercial heart.
"The bomb aimed at killing as many people as possible as the shrine is crowded at around 6 to 7pm," Police spokesman Prawut Thavornsiri told AFP early Tuesday (local time).
"The death toll is now 20 with 123 wounded ... of the dead, 14 were killed at blast site," he said, adding the bomb probably contained three kilograms of explosives.
Authorities have said the blast targeted foreigners, with Chinese, Hong Kong and Filipino citizens among the dead, while Singapore and Taiwan reported that some of their citizens were injured.
The area, which is at a major traffic intersection flanked by five-star hotels and upscale shopping malls, remained cordoned off early Tuesday as police tightened security, with hundreds of schools closed and checkpoints thrown up across the city.
As dawn broke police bomb experts photographed the blast site scouring for clues, an AFP reporter at the scene said.
The bomb was detonated at about 6:30pm (11:30pm NZT) in the middle of the city's peak hour, sending a fireball into the sky as commuters and tourists fled in panic.
"I heard a very loud bang, it made the whole building shake so I ran outside to see what had happened," Panupan Chansing, 20, a hotel worker at the nearby Grand Hyatt Erawan, told AFP late Monday.
"I saw bodies lying on the ground and I saw vehicles on fire. I feel very sad and sorry that this has happened to Thai people ... I'm scared."
Thailand's junta chief says authorities are hunting a male "suspect" seen on CCTV footage near the scene of the bombing.
"Today there is a suspect ... we are looking for this guy," Prayut said, adding the man was seen on closed circuit television at the blast site.
He also said he believed Facebook messages apparently warning of an imminent danger to Bangkok ahead of the bomb came from an "anti-government group" based in Thailand's northeast, the heartland of the kingdom's anti-coup Red Shirt movement.
"We are looking for them now, some of them are in Isaan (northeastern Thailand)," Prayut said.
Since 2006 Bangkok has witnessed repeated rounds of deadly political violence, flanked by two coups. Until Monday though, foreigners had rarely been caught up in the bloodshed.
The most recent coup in 2014 toppled the elected government of Yingluck Shinawatra after months of disruptive street protests.
Thailand is also fighting a decade-long insurgency in its southernmost Muslim-majority provinces that border Malaysia, which has seen more than 6400 people killed, mostly civilians.
Prayut's comments suggest the investigation is shifting towards anti-government groups loyal to the ousted Shinawatra family, rather than the southern Muslim militants.
The Red Shirts are a grassroots network of rural and urban poor that are loyal to Yingluck and her self-exiled brother, Thaksin Shinawatra, who was a previous prime minister.
Authorities have blamed them for a string of small explosions in Bangkok earlier this year, a charge their leadership has strongly denied.
They were also initially blamed by authorities for a car bomb on the resort island of Koh Samui earlier this year, but police were later forced to backtrack and subsequently blamed insurgents for that attack.
While hardcore Red Shirts have been known to launch attacks on security forces or government buildings, they have never before carried out a mass casualty bombing.
No one has claimed responsibility for the assault and security analysts expressed scepticism over the government's lightning move to cast suspicion on its opponents.
"Even if they (Red Shirts) are hell bent on bringing down the government, I just can't see them targeting a Hindu or any other religious shrine," said Zachary Abuza, an independent expert on Thai security.
"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.
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.
Junta officials said the attack was aimed at damaging the country's tourist industry, which is a rare bright spot in an otherwise gloomy economy, but it remains unclear who stands to gain from an attack of this scale.
"[The attackers] had the clear target of destroying our economy and tourism .... and discrediting the government," Defence Minister Prawit Wongsuwon 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.
Police have tightened security across Bangkok, with hundreds of schools closed and checkpoints thrown up across the city.
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, and Sukhondhapatipak said that the style of bomb was not similar to those used by insurgents in the south.
The attack drew quick expressions of grief from around the world, with UN Secretary-General Ban Ki-moon's office releasing a statement saying he was shocked.
Kiwi Marko Cunningham, a volunteer paramedic volunteering in the city, was among the first on the scene and said it was chaos.
"The problem was they were all in critical condition... they were literally, the word I have been using is shredded, literally like seeing something going through a shredder, the legs, the arms were hanging off the bone, broken, a lot of people were naked the bomb had blasted their clothes off. It was a mess. It was nasty, it was meant to hurt and kill many people."
He says he saw at least 14 people dead, many lying on top of the injured.
The New Zealand Ministry of Foreign Affairs and Trade (MFAT) has updated its travel advisory for the country and advises caution in most parts of Thailand, including Bangkok, "due to the threat of terrorism and potential for violent civil unrest". It recommends travellers register online with SafeTravel – the official advisory.
"The New Zealand Embassy in Bangkok continues to seek information on the nationalities of victims and casualties from the explosion at the Erawan Shrine in central Bangkok," MFAT said in a statement.
"At this stage there is no information that suggests New Zealanders have been killed or injured in the explosion. If you have concerns about a New Zealand family member in Bangkok, please try and make direct contact in the first instance."
There are currently 508 New Zealanders registered as being in Thailand, according to SafeTravel.
AFP / 3 News