One after another, the bombs went off, destroying shops and vehicles, engulfing buildings in flame and smoke and sending panicked shoppers and tourists fleeing.
By Monday, two days after the most coordinated bomb attacks in southern Thailand in years, the damage was clear: 13 people were killed, more than 300 wounded and the Thai government's policy to contain an eight-year rebellion by shadowy ethnic Malay Muslim rebels was again in tatters.
The bombs were hidden in pickup trucks in two cities 140 km (87 miles) apart, exploding within an hour of each other. Two went off in Yala, one of three Muslim-majority southern provinces at the heart of the insurgency that has claimed 5,000 lives since 2004.
Those explosions killed 10 people in a busy shopping street.
A third went off in the basement car park of the five-star Lee Gardens Plaza Hotel and shopping centre in Hat Yai, a bustling commercial centre that rarely sees such violence, just a few hour's drive from some of Thailand's best-known beach resorts. Rescue workers recovered three bodies from the hotel.
What's unprecedented was the scale of the operation ... and the ruthlessness in targeting large numbers of civilians, said Anthony Davis, an analyst at IHS-Jane's, a global security consulting firm.
The bombings add to a growing list of problems for Prime Minister Yingluck Shinawatra, a political novice who since taking office last August has faced problems on multiple fronts, from a flood crisis and entrenched political divisions to rising food prices and a struggling economy.
Yingluck pledged before her election to consider turning the three southern provinces into a special administrative zone with one elected governor, a sensitive subject in Buddhist Thailand where the government has long resisted the idea of handing more political power to its minority Muslims.
But Saturday's attacks in a city popular with Malaysian tourists might give her reason to reconsider that idea.
Violence in the three southernmost provinces has become routine, says Davis, but an attack at the heart of Hat Yai's tourist district on a Saturday afternoon was obviously intended to seize national and international attention and make a very brutal point: this is not 'business as usual'.
Images of the devastation - wrecked vehicles, smashed windows at fast-food chains, bloodied victims, plumes of black smoke - played prominently on television news broadcasts and were splashed on the front pages of newspapers, rare coverage of a largely forgotten but festering conflict that barely registers in faraway Bangkok.
BOMBERS' GOAL NOT CLEAR
Security forces appeared caught off guard. As they raced to the scene of the first blast in Yala, another bomb - explosives stuffed into a cooking gas cylinder - went off, leaving behind mangled wrecks of cars and a big crater.
The bombing in Hat Yai struck where it hurts most: a tourist centre. Among the dead was a Malaysian traveller. A one-month-old baby was critically wounded.
Yingluck has ordered police and troops to strengthen security in Hat Yai, 11 days ahead of an anticipated influx of tens of thousands of tourists, many from Malaysia, to celebrate Thailand's Songkran water festival.
With tourism vital to Thailand's economy, it is highly unlikely the government will extend to Hat Yai the state of emergency covering neighbouring Yala, Pattani and Narathiwat provinces, where more than 30,000 troops have been trying to crush the insurgency, with little success, and little sympathy from a population who largely resent the military.
The insurgents' goal is unclear. The three provinces were an independent Malay Muslim sultanate before being annexed by Thailand in 1909. It is assumed they want the territory back, or at least some kind of autonomy from Bangkok.
Resolving the conflict is a contentious issue and could put Yingluck on a collision course with the army, which favours military measures and hearts and minds campaigns rather than the government's quiet pursuit of some kind of dialogue.
Yingluck indicated on Monday there would be no immediate shift in strategy. (It's) a warning for us but not necessarily a sign we need to start talking about a change in our approach to the southern problem, she said in Bangkok.
Srisomphob Jitphiromsri, a Pattani-based political scientist with the Deep South Watch think-tank, suggested the latest bombings could reflect dissatisfaction with the government's policy, and perhaps disunity within the rebel movement.
The level of destruction and co-ordination of this latest incident was not something trends in recent months were indicating. It was not expected, he said.
It's likely we'll see an escalation in violence this month. There's internal division among the insurgents - some want a special administrative zone and others want complete autonomy - but none are happy with the government's policy.
(Martin Petty reported from Bangkok. Additional reporting by Amy Sawitta Lefevre and Orathai Sriring; Editing by Jason Szep and Robert Birsel)