The robbery of a Subway sandwich shop Tuesday night in Plainview is part of a pattern of knifepoint robberies committed by a masked man in Nassau and Suffolk counties during the past six weeks, police said Wednesday.

Wednesday, Suffolk police said they had identified at least three in the county that fit the pattern while Nassau police said there have been five such robberies and one attempted robbery in Nassau since Feb. 15.

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

Nassau police have stepped up patrols around similar businesses and on Wednesday, Northport Police Chief William Ricca said his department would provide extra patrols at the Carvel on Fort Salonga Road in Northport during business hours, with a special emphasis on evenings, when the robber has struck in the past.

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

Authorities investigating the robbery pattern have said they believe one male suspect may be responsible for the crimes because of the consistency in his clothing, build and the type of weapons used.

The man was described as 5-foot-6 to 5-foot-8, wearing a dark knit cap with a brim, a dark-colored scarf over his face, a dark-colored jacket, jeans, gloves and tan shoes.

Detectives ask anyone with information to call Crime Stoppers at 800-244-8477. All callers will remain anonymous, police said.

The other crimes fitting the pattern were:

Feb. 13, Carvel, 1075 Montauk Hwy., Copiague

Feb. 15, 9:12 p.m., Dunkin’ Donuts (attempted robbery), 4007 Merrick Blvd., Seaford

Feb. 15, 9:40 p.m., Carvel, 319 Northwest Dr., South Farmingdale

March 20, Subway, 1195 Sunrise Hwy., Copiague

March 21, 9:55 p.m., Carvel, 4246 Hicksville Rd., Bethpage

March 26, 8:20 p.m., Carvel, 810 Carman Ave., Westbury

March 28, 5:53 p.m., Subway, 347 Old Country Rd., Carle Place

April 1, Carvel, 290 Ronkonkoma Ave., Lake Ronkonkoma

— With Nicole Fuller and Michael O’Keffee

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