Major Edgardo Amores, spokesman of the Army’s First Infantry Division, said the suspects were on board two pump boats as they strafed the power barge off Tabuk town for about five minutes past 10 p.m.
Troops of the Army’s 4th Special Battalion who were in the vicinity immediately returned fire, but the gunmen immediately fled.
Additional forces were later deployed, and checkpoints were also established within city limits to prevent further eventualities.
The damaged power barge has a 7.2-megawatts capacity.
Reports said power barge engines were shut down after incident, which led to power outage in Isabela City.
Amores said power in some parts of the city were already restored as of Tuesday.