(CNN) With most of Puerto Rico in the dark Wednesday night, Gov. Ricardo Rossello said in a tweet that he has suggested Puerto Rico's Electric Power Authority cancel its contract with a subcontractor that caused an island-wide power outage.

An excavator operated by D. Grimm, a subcontractor for Cobra Acquisitions, apparently caused the blackout, which originated at a major transmission line running between Salinas and Guayama in the southeast, according to the authority.

The same company was responsible for an outage that affected 870,000 customers after a tree fell on a power line last week, PREPA said.

Mammoth Energy, Cobra's parent company, said workers were removing a fallen tower when the machine got too close to an energized line and an electrical ground fault caused the outage.

As of 8 p.m., only 334,000 customers in the US commonwealth had electricity again. Power was to be restored to customers who had electricity before the latest outage within 24 to 36 hours, the authority said.

Read More