A soldier, pale-faced and soaked after the rains, is overcome with sleep behind an empty shack, seemingly oblivious to the barrage of rockets and artillery fire pounding the jungles around him. An armoured car, mounted with a portrait of Cambodia's smiling King Norodom Sihanouk alongside a 50mm machine gun, rumbles towards the horizon firing spurts of crackling bullets at unseen targets, prompting chilling squeals from the pigs running loose in the street.
Through the bedlam, a moped comes into earshot, picking its way through the water-filled ruts that pock-mark the route to the Thai border. Huddled together on the saddle are three men in tattered battle fatigues. One of them, propped up by his comrades, is dripping with blood from a shrapnel wound that has blown off half his jaw. His friends leave him at the border, pick up his Kalashnikov, and turn to defend their final bastion.
O'Smach, where 500 or 600 royalist fighters are pinned against the frontier with Thailand, may be little more than a deserted, handkerchief-sized corner of Cambodia. Its tin shacks, once roadside stalls, stand emptied of stock. It hardly seems worth fighting for.
But for the supporters of Prince Norodom Ranariddh, who was ousted as co-premier in a bloody coup d'etat last month by his powerful rival and coalition partner, Hun Sen, O'Smach represents a last breath of resistance, their only hope of staking a claim in Cambodia's new equation of power.
Out-gunned and out-numbered, the royalists were cornered here two weeks ago, and have held on to the town against the odds with the help of Khmer Rouge fighters. Few expect the rag-tag of demoralised royalists to hold on much longer. The fact that the town has not capitulated already, say Thai military officials, is by virtue only of the hundreds, perhaps thousands, of landmines the royalists have scattered on the jungle slopes which lie between them and the forces of Hun Sen, waiting on the plains below.
"We will never be moved from this place," royalist commander General Nhiek Bun Chhay told The Independent by telephone from his O'Smach camp, as the mortars rained down, "as long," he added, "as we have enough ammunition and food."
Supplies of artillery shells seem plentiful. From one position yesterday, royalist gunners fired 46 heavy explosive rounds into the jungles just two kilometres away, in a bid they said to kill the hundreds of government troops who had been on the point of entering O'Smach.
Hun Sen's men, well-trained and equipped, have been returning fire blow for blow, but their efforts have been hampered by the proximity of the royalists to the border. At least two shells landed inside Thailand yesterday. No one was injured, but the Thai armed forces fired warning flares, threatening to strike back with "tremendous force" if there were any more incursions.
That is a prospect relished by the dissident Cambodian MPs encamped as a virtual government-in-exile at a plush Thai hotel, well away from the fighting.
They have been lobbying Thailand for support, aware that whether the administration in Bangkok likes it or not, the future of the royalist military struggle in north-western Cambodia depends largely on the de facto support offered in the sanctuary of the Thai border.
Already, Thailand has extended humanitarian assistance to more than 35,000 Cambodians who streamed across the border to escape the fighting last week. At the refugee camp five miles from Chong Chom, plastic sheeting and emergency food rations have been handed out by the Thai military and aid organisations, while medical teams treat cases of malaria and dysentery.
The people are grateful: "I wish Cambodia could be at peace like Thailand," said Mira, a young mother who fled with her child as their village came under attack. But the Thais, though efficient, appear weary and are shying away from too much publicity: sensitive, perhaps, to an unspoken suspicion that they are in danger of taking sides in Cambodia's conflict, a suspicion hardly dispelled by the sight of full rice sacks being carried past the border fence by royalist soldiers at the weekend.
Despite its history of covert involvement in Cambodia's troubles, increased business interests in Phnom Penh and affable ties with Hun Sen suggest on the face of it that Thailand has little reason to play anything more than a concerned neighbour.
But the Thai authorities are aware that once this latest round of fighting ends, stability is unlikely to return to the border region. Once the royalists are defeated, Hun Sen has vowed to move against the Khmer Rouge stronghold of Anlong Veng, which could send tens of thousands more Cambodians fleeing onto Thai soil.