An ambulance pulls up to a primary school hastily converted into a field hospital in suburban Hanoi, and medics rushed a coughing, writhing patient on a stretcher inside for treatment. Army doctors succeed in putting him on a ventilator within minutes, but they knew there are many more patients to come. Probably more than they can handle.
This is the nightmare scenario of an influenza pandemic, affecting not only Vietnam but much of the world. But on Sunday, at least, it was only a drill.
Vietnam's Health Ministry, along with the army, police and various city agencies, staged the country's first practice for what could happen if the H5N1 strain of bird flu virus becomes more communicable among humans, and looses a pandemic that experts fear could kill millions of people.
Vietnam is all-too aware of the dangers. Of the 64 people who have died worldwide of H5N1 since 2003, two-thirds have been Vietnamese. H5N1 is already endemic among the country's poultry population, and Vietnam is considered a likely pandemic ground zero if the virus mutates into a form that can pass easily from human to human.
The scenario practiced Sunday was of an outbreak of bird flu among 30 families in one Hanoi neighborhood, with evidence that the virus was jumping between humans as easily as regular human-flu strains.
Attempting to stop the spread of the virus, a battalion of health workers wearing protective clothing, goggles and rubber boots spread out around the neighborhood spraying disinfectant on buildings. Police sealed off roads and made anyone coming in or out walk through a sterilizing chemical pool.
In reality, stopping the spread of an airborne virus would be extremely difficult, even if the outbreak were detected in time. But Peter Horby, an epidemiologist with the World Health Organization in Vietnam, said containment is still the weapon of first choice even if no one knows if it will work.
"We just do not know, but we have to try. You cannot assume that it wouldn't work and just give up," said Dr. Horby. "I think you have to prepare to try to contain it at an early stage, and if that fails, still be able to deal with a pandemic on a national and global level."
The WHO has called on all countries to prepare for what it says is an inevitable new flu pandemic, whether it is caused by H5N1 or some other virus. Yet only a fraction of the world's countries have developed a pandemic plan. Mr. Horby called Vietnam's preparations on Sunday impressive.
"They have got a plan. They have involved lots of different agencies. The broad brush, it looks very good. I think it is just done to the detail, really, and how you'd implement it in practice," he said.
Vietnam hopes it will never have to put its plan into practice. But here at the epicenter of bird flu cases so far, there is little other choice than to prepare.