A new email threat made against Mayor Bill de Blasio and New York City schools received Thursday night is “noncredible,’’ NYPD officials said.

“There is no substance whatsoever. We knocked it down as fast as we got it,’’ said Police Commissioner William Bratton at a Brooklyn news conference Friday afternoon.

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Several private schools also received the same threatening email. Police officials would not elaborate on the contents of the threats.

John Miller, deputy commissioner of intelligence and counterterrorism, said the emails resembled the same one issued in December that triggered Los Angeles city officials to shut down their schools. The same email threat was made to New York, but officials here deemed it also “noncredible’’ and schools remained open.

“It’s a rerun from the same authors or authors. . . . It’s people who enjoy watching others jump through hoops,’’ Miller said. He said the email threat is on the same level as that of pulling a fire alarm or calling in a bomb scare.

The “annoyance letters,” said Miller, are being investigated by the FBI, which also disclosed that a new email address was used with the new email threat. “The FBI has a lead on it,” Miller said.