CARACAS/PUNTO FIJO, Venezuela (Reuters) - Venezuelan state-run oil firm PDVSA has been unable to resume crude exports at its primary port since last week’s blackout, according to people familiar with the matter, indicating that the country’s massive power outage is crippling the OPEC nation’s principal industry.

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Power remained patchy in most of the country after a blackout on Thursday that the government of President Nicolas Maduro claimed was a U.S.-backed act of “sabotage” on the country’s principal hydroelectric dam.

His critics insist it is the result of more than a decade of corruption and mismanagement.

Authorities have given few explanations about why the blackout occurred and how long it might take to resolve, spurring fears it could be indefinite.

PDVSA has launched a contingency plan to restore power to the Jose port, according to one source. The state of Anzoategui, where the port is located, has had only intermittent electricity since Friday, the source added.

“It has been totally halted since the blackout. It has affected all of Jose’s oil installations,” another source said, adding that a restart would be costly and require power lines to be replaced.

PDVSA did not immediately reply to a request for comment.

No oil export tankers have left Jose since March 7, according to Refinitiv Eikon data. There were a few shipments between domestic ports on Saturday, when power briefly returned, but another outage that lasted through Sunday halted operations again, according to the data.

The power outage also affected the Puerto la Cruz refinery in Anzoategui, which was already operating at minimum levels. The country’s crude upgraders, which can convert up to 700,000 barrels per day of Orinoco Belt heavy oil into exportable grades, also operated at minimum levels due to the lack of power, the sources said.

Blackouts are not unusual in Venezuela.

Incidents stemming from problems at the Guri hydroelectric dam have briefly disrupted oil activities at fields that depend on the grid, which are mainly located in western Zulia State, rather than the Orinoco belt. Many fields, refineries and ports generate their own power.

But the current outage has been much more widespread and prolonged than those in the past. The status of the generators that PDVSA and its private partners use in upstream activities was unclear.

PDVSA has said it has activated a contingency plan for its gas stations that do not have their own power generation, but has not provided a general update on domestic fuel supply.