Authorities in Washington state say it's too dangerous to send rescuers into a mudflow that is "basically like quicksand."
The mud was so thick and deep that searchers turned back last night after attempting to reach an area where voices had been heard crying for help. At the time, rescuers were using thermal imaging cameras to locate them.
Authorities say the slide wiped out one neighborhood of 28 to 30 homes, and blocked about a mile of State Route 530 near the town of Oso, about 55 miles north of Seattle.
The mud was reported to be about 60 feet deep in some areas.
At least three people were killed. Several others, including an infant, were critically injured.
At least 18 people are unaccounted for.
Authorities say rescue attempts are dangerous because the mud flow is still moving, and has a quicksand like consistency. Water that has been backed-up is also causing flash flooding concerns.
As authorities try to determine how to get responders on the ground safely, helicopters will be flying over the area looking for people who may have been able to get out on their own and any other signs of life.
Authorities say heavy rain earlier this month saturated the ground and may have caused the slide.