Authorities say a vehicle hit 24-year-old Erika Hughes, who was crossing Mastic Road just south of Riverside Avenue around midnight.
The driver did not stop at the scene, and Hughes died a short time later.
The fleeing vehicle is described by witnesses as a dark-colored truck, possibly a pickup truck, tow truck, or other utility vehicle.
Witnesses say the vehicle, which may have front-end damage, fled southbound on Mastic Road and eventually turned east.
Detectives are asking anyone with information to call the Seventh Squad at 631-852-8752 or anonymously to Crime Stoppers at 1-800-220-TIPS. All calls will remain confidential.