There had been nonstop rain for several days in the hills in Minh Phu Commune in Soc Son, about 30 km from downtown Hanoi.
At around 10:40 a.m. Friday more heavy rains triggered the flash floods down the 400-meter Dong Chum hill.
In the kilometer-long road, there are four resorts, and guests' cars parked on its two sides bore the brunt of the landslide.
Binh, whose car was among those buried, said when the flash flood occurred he and several friends who had been inside a resort heard a rumbling noise and ran out only to see rocks and mud flowing over cars.
"We were helpless and could not do anything but watch," he said.
Of the 13 damaged vehicles, five were completely buried while the others were partially stuck in the debris.
The Mercedes-Benz was submerged in earth and rocks up to its wheels.
By afternoon the rain had stopped but not the water flowing downhill.
According to locals, this was the first ever flash flood in the area.
People wade through the mud to leave a resort.
Since July 28 Hanoi and nearby localities have received heavy rains under the influence of a low-pressure trough.
On July 31 and August 1 many urban areas in Hanoi were under 30-50 cm of water.
The aftermath of the flash flood.
The National Center for Hydro-Meteorological Forecasting said Soc Son received around 60 mm of rain on Friday morning compared to 130 mm in Vinh Phuc and 80 mm in Tuyen Quang.
The north should expect more rains in the next four days, it said.
