When the accident happened, local spotted white smoke and an unpleasant smell coming from a gas extraction station on An Phu Tay Street in Binh Chanh District before seeing many workers running out, struggling to breathe and even vomiting blood.
The gas killed many plants, pets, livestock and poultry nearby and prompted a mass evacuation of more than 1,000 students and locals.
According to eyewitnesses, the pipe broke as workers were extracting the gas from a truck at the station, causing the leak.
The four victims included a passer-by, the truck driver and two workers. They are now in stable condition.