The number of victims of a suspected serial killer on New York's Long Island has doubled in the past week following the discovery of three more corpses along a remote beach highway.

The remains of eight victims have now been found just steps from Ocean Parkway, a highway leading to popular Jones Beach, about 72 kilometres east of New York City. The bodies of four missing prostitutes were found in December while investigators were searching for another missing woman who worked as an escort and was last seen in the area nearly a year ago.

Emergency personnel search the thick brush on the side of the road near Oak Beach, N.Y. on Monday. Seth Wenig/Associated Press

The disappearance of that woman, Shannan Gilbert of Jersey City, New Jersey, remains a mystery, although Suffolk County Police Commissioner Richard Dormer said Monday that because detectives have been conducting an ongoing search for her, they already have her DNA and other forensic information, which should accelerate the identification process.

Last week, investigators found a fifth body about 1.5 kilometres east of where the first four were located. That discovery prompted police to resume a widespread search of a 11-kilometre stretch of the north side of the highway on Monday, a search that yielded the remains of three additional victims.

Investigators resumed their search, which included police academy cadets, volunteer firefighters with extended ladder trucks, and cadaver dogs, on Tuesday. Investigators faced rainy, windy and foggy conditions. The marshy terrain features a metre-tall tangle of sea grass punctuated by scrubby pine trees. At least 20 police officers have gotten poison ivy and the area is infested with deer ticks, officials said.

The identities of the most recent four victims have not been released and police have yet to even describe their gender. The New York City medical examiner's office is assisting Suffolk County in helping determine the identities.

"We still believe that Shannan Gilbert is in this area," Suffolk's Chief of Detectives Dominick Varrone told reporters Monday.

Victims worked as escorts on Craigslist

Gilbert, 24, was last seen in Oak Beach on May 1, 2010, after apparently meeting a client she had booked through Craigslist. The bodies of the four other women, who worked as Craigslist escorts and were in their 20s, were found along the same highway by police searching for Gilbert.

The latest discovery was about 1.5 km east of where the other four were found. The remains of the four dead women were strewn about 450 metres apart.

Gilbert had arranged to meet a client in Oak Beach, a gated seaside enclave. A resident has told authorities a woman believed to be Gilbert came to his door around 4:45 a.m. May 1, pleading for help. The man said that when he tried to call police, the woman fled.

Moments later, an unidentified man in a sport utility vehicle drove past the house and said he was looking for the woman, but then took off. Neither the woman nor the man was seen by the neighbour again.

The client Gilbert had arranged to meet was investigated but is not believed to be a suspect in her disappearance.

Authorities have identified the four victims found in December as Amber Lynn Costello, 27, originally of Wilmington, North Carolina; Megan Waterman, 22, of Scarborough, Maine; Maureen Brainard-Barnes, 28, of Norwich, Connecticut; and Melissa Barthelemy, 24, of Buffalo, New York. All were last seen planning to meet clients for sex booked through Craigslist, police have said.

Detectives suspect a serial killer but so far have no suspects.