In a shot across the bow of Mayor de Blasio, Westchester County Executive Rob Astorino is opening an office in Midtown in a bid to lure away New York City businesses.

“We are opening a new Westchester Economic Development office at 125 Park Avenue . . . right across from Grand Central Station,” Astorino will say Wednesday in his annual State of the County address.

“The purpose for the office is to aggressively promote Westchester’s many assets, offerings and competitive advantages to companies and entrepreneurs looking to relocate, expand or start businesses.”

Astorino was the Republican candidate for governor last year.