The pre-dawn landslide also left some 30 injured as it tore through a ravine in Salgar, a municipality of some 20,000 people in the department of Antioquia.
The rush of mud and water "tore down everything in its path," Salgar Mayor Olga Osorio told journalists.
The small town of Santa Margarita was practically "wiped off the map," she said.
"We have 33 dead, but that figure could increase," said Ines Cardona, director of the regional disaster response agency.
Authorities said rescue workers were having difficulty accessing the area. More emergency teams and medics are en route.
President Juan Manuel Santos tweeted that "those affected will receive all our support.