Almost 7,000 NYPD cops began deploying Saturday afternoon to guard against any terrorist threat against the millions gathering to watch the Macy's Independence Day fireworks show.

The 39th annual Macy's Independence Day fireworks show was due to begin about 9:20 p.m. with about 50,000 pyrotechnic effects shot off from five barges in the East River off lower and midtown Manhattan.

Police Commissioner William J. Bratton said Saturday that there's no specific threat, but he's most concerned about so-called lone-wolf terrorists inspired by Islamic State via social media.

"It's not so much what we know that concerns us but what we might not know," Bratton told reporters.

Brattona addressed about 200 officers beginning their shifts under the FDR Drive near 23rd Street as a police helicopter roared, sharpshooters with assault rifles and binoculars watched above and radiation-detection boats maneuvered in the river behind.

The overall number of cops assigned to the detail is the highest since 2008, the last time the fireworks barges were arrayed along as lengthy a stretch of the East River, Chief of Patrol Carlos Gomez said.

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In years when the show was staged on the Hudson River, New Jersey authorities contributed to the counterterrorism effort.

Deputy Commissioner for Counterterrorism John Miller said Islamic State terrorists would be content with a successful small attack, rather than an al-Qaida-style reprise of the Sept. 11, 2001, attack.

"You're looking at the potential for a small-scale attack with nearly zero cost in terms of finance, very little pre-operational preparation where you may only kill one or two or three people, but they understand that if they get more than one of those, if they can get that in rapid succession they can have a significant impact," Miller said.