A pair of duck hunters caused a minor scare at the Pilgrim Nuclear Power Station in Plymouth early Saturday when security personnel at the plant heard gunfire coming from Cape Cod Bay, officials said today.

According to the Nuclear Regulatory Commission and Plymouth police, the two hunters were licensed to carry firearms and to hunt, and were not inside the marked-off security zone surrounding the plant on the bay side of the facility operated by the Entergy company.

But the operators at the Plymouth plant did not know they were hunters right away and after hearing gunshots coming from the waters nearby, plant security officials reported an “unusual event’’ to the NRC, the Coast Guard, and Plymouth police.

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Responding police quickly identified the hunters and verified they were in the area legally, Plymouth Police Chief Michael E. Botieri said.

Because nuclear power plants are sensitive locations, security and law enforcement officers respond quickly and thoroughly to every perceived threat, no matter how small, NRC spokesman Neil Sheehan said.

The plant was already shut down at the time of the shooting, Sheehan said, because workers were fixing a water pump that had been leaking.