Long Island’s serial knifepoint robber has struck again.

Nassau Police Robbery Squad detectives linked the knifepoint robbery of a Westbury sandwich shop Saturday night to a spate of similar holdups in Nassau and Suffolk counties since mid-February, Nassau Det. Lt. Richard LeBrun said Sunday.

Police suspect the same masked man has robbed or attempted to rob a total of nine Carvel and Subway shops in the past two months in Nassau and Suffolk. In each holdup, the suspect displayed either a knife or a machete, demanded money and fled with cash.

LeBrun said cops continue to step up their patrols around similar businesses and advised owners to keep their stores well lit and to remove signage from windows so officers have clear views inside.

The Crime Stoppers reward in the case is $10,000, authorities said, with $5,000 each from both Nassau and Suffolk Crime Stoppers.

In Saturday night’s robbery of a Subway sandwich shop at 890 Old Country Rd. in Westbury, a masked man displayed a knife at about 8:20 p.m., demanded money from the cash register and fled with an undisclosed amount of cash, Nassau police said.

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The suspect was last seen walking south on Bowling Green Drive.

There were no injuries reported, police said. The suspect was described as 5-foot-6 to 5-foot-9, wearing a dark knit hat with a brim, a dark jacket, a dark scarf covering his face, jeans and gloves. There were two employees and no customers inside the store at the time of the robbery, police said.

The suspect’s description was nearly identical to that of the masked man who held up a Subway sandwich shop Tuesday night, about five miles east on Old Country Road in Plainview.

In that holdup, which police said occurred at about 7:50 p.m., a man with a large knife entered the Subway at 1022 Old Country Rd. and demanded money, Nassau police said. The clerk opened the register and the man grabbed an undisclosed amount of cash and fled.

Police said the Tuesday robbery fit the pattern of three other robberies and one attempted robbery committed in Nassau since Feb. 15. In Suffolk, police said three robberies committed since February also fit the pattern.

The suspect has alternately used a large kitchen knife or a machete during the robberies, police said.

Detectives request anyone with information regarding this incident to call Crime Stoppers at 800-244-TIPS. All callers will remain anonymous.