One mistake by a clumsy crane operator caused a 10-hour blackout over about a third of Vietnam, exposing the fragility of the nation's power grid.

State electricity company EVN said in a statement Thursday that the blackout occurred Wednesday after the crane operator knocked a tree down onto the main north-south high voltage power transmission line.

The outage covered 22 of Vietnam's 63 provinces. It was not clear how many people were affected, but the loss of power forced scores of garment and seafood factories to close, and traffic was snarled in major cities as traffic lights failed.

State-owned newspaper Thanh Nien reported that the incident cost EVN $700,000 in lost revenue.

Vietnam's power generation sector needs modernizing, but low tariffs are making foreign investors wary about returns.