Most residents were sleeping when the landslide hit the municipality of Salgar around 3am on Monday, burying a large area in mud and debris.
Aerial images showed a broad river of mud that had inundated a large area, dragging houses and trees along with it.
Emergency teams, rescue dogs and humanitarian aid have been sent to the affected areas. The area had been hit by several days of heavy rain.
Colombia's tropical climate and mountainous landscapes make it prone to landslides. Heavy rains in Columbia in 2010-11 left 1,374 people dead and destroyed more than 100,000 homes.