Nearly three million people are without electricity in south-western Colombia after suspected rebel attacks.
Officials said they believed bomb attacks on a number of electrical towers may have caused the blackout which is affecting three provinces.
Energy company Isa said it was trying to import power from neighbouring
Attacks on infrastructure have declined in recent years, but the main rebel group has been stepping up pressure.
Rebels from the Revolutionary Armed Forces of Colombia (Farc) and drug traffickers are known to operate in the region.
An unnamed army official said he thought the Farc had used dynamite to blow up three 50-m (165-foot) tall towers.
Isa spokesman Gabriel Gallon said that was the "most probable" cause of the outage which left Cauca, Narina and Putumayo without power.
Left-wing rebels have been fighting state forces in a four-decade conflict which also involves right-wing paramilitary groups.
Tens of thousands of civilians are known to have been killed in the conflict.