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“Sharknado” is eating up the box office!

A one-time showing of the campy shark flick sold out at a Union Square movie theater 24-hours in advance, prompting movie executives to add another screening — which sold out even faster.

“This is unheard of for a made for TV movie — no one thought this movie would do so well,” said Harry Medved, a spokesperson for movie ticket seller Fandango. “It has the trappings for Rocky Horror -type cult movie following,” he said.

He added film honchos are now considering adding a third screening in New York City tonight.

Fans have so far bought more than 600 tickets in for two 12:05 am showings at the Regal Cinemas in Union Square — the only New York City location showing the film.

A late-night screening of the so-bad-it’s-good movie — which centers on a tornado of sharks that strikes L.A. — will also show in Edgewater, N.J.