A pair of thieves on a motorcycle swiped a $10,000 necklace and a cellphone from an off-duty cop in Manhattan over the weekend, authorities and police sources said Monday.

The 40-year-old officer, who works in the Bronx, was walking home around 1:10 a.m. Sunday when the bikers approached him at Broadway and Cumming Street in Inwood, authorities said.

The rear passenger hopped off the motorcycle, flashed a black gun and snatched the pricey chain and phone, cops said.

The officer was uninjured, and the suspects were still on the loose Monday morning.