Three people are dead after a massive landslide in Washington State that also injured nearly a dozen others, according to authorities.

Authorities said at least six houses were swept away in the slide that occurred just before 11 a.m. Saturday near Mount Vernon about 200 kilometres south of the Canadian border.

A total of eight people were rescued by a team of nearly 100 search-and-rescue volunteers and then treated at area hospitals. Snohomish County spokeswoman Shari Ireton said a 6-month-old infant was among those injured.

The slide of dirt, trees, rocks and other debris was at least 135 feet wide and 180 feet deep. Police said the conditions were so treacherous that one of the search teams had to be rescued.

Paul Falcao witnessed the tragic slide from his vehicle.

“I was the third car behind a truck with a boat, and that’s when I just saw the darkness washing everything off the road,” he said. “I’m not sure if the truck made it through, but it didn’t look like [it].”

Authorities believe the slide was caused by ground water saturation from recent heavy rainfall.

The landslide blocked State Route 530 near the town of Oso, about 55 miles north of Seattle. Also blocked is the North Fork of the Stillaguamish River, which is expected to cause flooding in the area.

Reverse 9-1-1 calls went out to residents in the area warning them of flooding upstream from the slide as well as downstream should the river breach.

With files from the Associated Press