A car bomb has exploded in the centre of the Colombian Pacific port city of Buenaventura, killing at least six people, officials have said, BBC reported.
More than 30 people were hurt by the blast near the mayor's office and the local public prosecutor's building.
There was no immediate claim of responsibility for the attack, though the army blamed left-wing Farc rebels.
Armed groups and drug traffickers are active in the western port, which lies on a key cocaine-smuggling route.
The explosion, which officials said occurred at about 0930 (1430 GMT), caused widespread damage to the city centre.
"This is an unfortunate terrorist act," said army commander General Freddy Padilla, adding that he suspected it was the work of the Revolutionary Armed Forces of Colombia (Farc).
The governor of Valle del Cauca province, Juan Carlos Abadia, said the car had been left outside the government buildings overnight.
President Alvaro Uribe, who leaves office this August, has pursued a tough security policy against the rebels during his years in office.
They have been put on the defensive, but they are still able to carry out attacks. In recent months, the Farc has carried out a number of raids on military posts in Valle del Cauca in particular, officials say.
Buenaventura, which has easy access to the coast, has over the years seen battles between guerrilla groups, drug traffickers and paramilitaries for control of lucrative smuggling routes.
Wednesday's car bombing was the most deadly in Colombia since September 2008, when four people were killed in Cali, the capital of Valle de Cauca.