Animal rights activists have shared the video in a bid to raise awareness about the cruel trade
Experts say the helpless animals would be force-fed, bludgeoned with bats then dropped into boiling water in the belief their meat grows tastier the more they suffer.
Meanwhile, another previously unseen clip from a Hanoi meat market shows a pile of butchered dog carcasses.
Eating dog meat is considered be a source of strength, curing illness and boosting male libido in the South-East Asian nation.
But opposition has mounted of late, with growing numbers of animal rights groups shining a light on the illicit yet unregulated industry.
Australian Michele Brown, the CEO of Fight Dog Meat charity, said: “In Vietnam, it’s believed eating tough meat makes a tough man.
“Many think dog meat boost’s a man’s libido, helps their joints and even cures illness. But none of this is scientifically proven.
“The preference is for tough meat, it’s like the opposite of meat eaten in the West.
“So they think by terrifying the dogs, they flood them with adrenaline and make the meat tastier.”
Unlike the superstitious cat meat trade that recently grabbed headlines, dog meat is mainstream in Vietnam.
Reports suggest an estimated five million dogs – many snatched from loving homes – are eaten annually with Hanoi serving as the most lucrative market.
Ironically, while the number of dog restaurants is on the rise in Vietnam’s capital, pet ownership is also growing and driving a booming dog theft industry.
Michele said dogs are often smuggled in tightly-packed vans like the one in the footage, but added that it’s rare to be caught on camera as they normally travel at night.
She said a horrified activist stumbled upon the Hanoi-bound truck by chance.
Both pieces of footage were filmed in 2016 but Michele is now sharing them with the media in a bid to raise awareness.
Michele said: “They were on a rural back road when they heard the wailing. They were horrified by what they saw and told me it still haunts them.
“These dogs are often snatched under cover of darkness. They are stunned or poisoned, then have their stomachs pumped to boost their value.
“Many die but the survivors are sold to slaughterhouses, restaurants or markets like the one I captured in Hanoi.
“This is why awareness is vital. We must pressure the government from the sidelines to break the cycle and shut the trade down.
“These animals deserve to be protected by the laws of the land.”