At least 37 people were injured in Monday's landslide in the municipality of Salgar, about 60 miles (100 kilometers) southwest of Medellin, President Juan Manuel Santos said.
Rescuers are searching for survivors, he said, but it isn't clear yet how many people are missing.
"People were just screaming everywhere, and I ran to help, but the river was impassable, and all the bridges were covered," survivor Leon Dario Restrepo told Colombia's RCN network
, recounting how he rescued a boy from the river just after sunrise Monday.
Jorge Quintero told RCN he felt his house shake.
"My family left, and when we left, we were in the middle of the landslide. It carried away a house ... and we were in the middle, and frightened," he said. "I said to my wife, 'Let's hug and hope to God that it doesn't take our house and we are saved.' "
Another survivor told Teleantioquia that debris started coming down the mountains at about 2 a.m.
"We ran outside to the road and went into the chapel, and the lights went out and we were in the dark," he said. "Then we looked with flashlights and saw that everything was gone."
Santos declared a state of emergency in the area, saying that the government would provide new housing for those who lost their homes, bring in heavy equipment to remove debris and support victims' families.
Antioquia Gov. Sergio Fajardo shared photos of the disaster on Twitter and expressed his condolences.
"All the teams are coordinating," he said, "every one with responsibility and a place. We will come out of this well. Solidarity. Thank you."