"At 9:45 am (1445 GMT) Buenaventura was left without electrical service," read a statement from the power company, the Energy Enterprise of the Pacific (EPSA).
A military overflight located the destroyed electricity tower some 27 kilometers (18 miles) from the urban center of Buenaventura, officials said, after two large explosions were reported.
The port of Buenaventura, Colombia's largest, handles most of the nation's foreign trade.
The attacks notwithstanding, the Marxist rebels with the Revolutionary Armed Forces of Colombia and the government are in peace talks dating back to November 2012, to end a decades old civil war, AFP reported.
The conflict has killed some 200,000 people and uprooted more than six million since FARC launched its Marxist-inspired guerrilla insurgency in 1964.