Surveillance video shows the man -- wearing a black jacket, jeans and an orange shirt -- jumping into the Hudson River just before 9:30 p.m.
"He jumped off the dock, flailed and disappeared," a responder said.
Divers were in the water soon after, as New Jersey State Police and the NYPD sent boats to join borough police.
Click here to follow Daily Voice Cliffside Park-Edgewater and receive free news updates.