Officials warned that security forces had been authorised to shoot looters and arsonists breaking the curfew after many red shirt protesters failed to surrender to the military following the incursion into the camp.
On Thursday, fires were still burning in buildings set ablaze in Bangkok the previous day amid sporadic bursts of gunfire.
A special police unit entered a temple inside the former protest site where several hundred Red Shirt supporters, most of them women, old men and children, had sought shelter in recent days. Six bodies were seen at the complex, but Asssociated Press photographers said there was no resistance at the temple as police took away the group to a nearby police station.
Six key red shirt leaders handed themselves after the military offensive on Wednesday, but many of their followers launched arson attacks across the Bangkok in protest at their treatment by the military.
Among the buildings set on fire as the red shirts retreated from their protest camp were the Bangkok stock exchange building and the Central World mall, the second-largest shopping centre in Southeast Asia.
The offices of state-run Channel 3 television were also set ablaze, forcing the evacuation of its executives by helicopter. Police rescued the rest of the staff.
The English-language Nation and Bangkok Post newspapers evacuated their staff after threats from the red shirts while a large office building down the street from the Bangkok Post office was set alight.
Unrest also spread to Thailand's rural north and northeast, areas that are seen as strongholds of red shirt support.
Local media reported protesters set fire to government offices in Udon Thani and vandalised a city hall in Khon Kaen.
Udon Thani's governor asked the military to intervene. TV images showed troops retreating after being attacked by mobs in Ubon Ratchathani.
Tony Birtley, Al Jazeera's correspondent in Bangkok, confirmed that violence had spread.
"A contact of mine phoned me from Chiang Mai [in the north] saying that fire engines were set alight, property was destroyed and barricades were set up there, so the violence is spreading."
Against this backdrop, Thaksin Shinawatra, the country's ousted prime minister whom many of the red shirts support, said he feared a military crackdown could lead to guerrilla warfare across the country.
"There is a theory saying a military crackdown can spread resentment and these resentful people will become guerrillas," he told the Reuters news agency by telephone.
|Officials warned that the army had orders to shoot looters or arsonists on sight [AFP]
Thaksin, who is accused by the government of bankrolling the protests and inciting unrest, denied he had undermined peace talks, saying he was not the "mastermind of the terrorists".
Larry Jagan, a Southeast Asia analyst based in Bangkok, told Al Jazeera that violence could spread as a result of the crackdown.
"The depth of mistrust and hatred [between red shirts and the government] has been escalated by the military reaction yesterday, so it's going to be very hard for any kind of reconciliation."
"I think what we are going to see is this kind of violence escalate, but not in Bangkok, throughout the north and northeast. Already, red shirt leaders had warned beforehand that if they were dispersed forcibly, they would bring the country to civil war."
"I think, although civil war might be too strong a word, we are going to see that kind of violence, that kind of distrust and that kind of division."
Wednesday's crackdown began with about 100 soldiers armed with automatic rifles and shotguns, along with several machinegun-mounted armoured personnel carriers, breaching the red shirts' barricade at the southern end of their protest site in Bangkok's Rachaprasong neighbourhood.
The armoured vehicles repeatedly rammed the barricade, made up largely of tyres, sharpened bamboo poles and razor wire, before breaking through the flattened structure.