Two police officers and four civilians died, with at least 18 more people wounded, when two explosives were set off in the Pacific port city, a police spokesman said.
Saulo Quinones, the Buenaventura mayor, said: "The police were drawn in by a fight between two men. As they were approaching, one bomb went off and then a second that ended with this tragic result."
Authorities say
Utilising millions in
Left-wing rebels
Despite government efforts, the Revolutionary Armed Forces of Colombia (FARC), the country's largest left-wing rebel group, is still strong in rural areas.
US and Colombian officials say FARC is a drug-trafficking terrorist organisation.
A car bomb destroyed most of a milk storage plant run by Nestle, a Swiss company, on Wednesday after FARC killed five officers in a bomb attack on a police truck near the border with
More than 600 troops and police were killed in combat last year and thousands of people are still forced from their homes each year by fighting between state forces and rebels.