An off-duty Jersey City police officer and another man beat a man unconscious and then continued to pound away in downtown Hoboken early Sunday morning, police said.

Erik Castro, who has been on the police force for a little more than a year, and Kely Nunfio, both 24, were each charged with aggravated assault in the incident in the area of First and River streets, Hoboken police Lt. Edgardo Cruz said.

Castro has been suspended without pay, Jersey City police spokeswoman Kimberly Wallace-Scalcione said.

Hoboken police responded to the report of a fight at 2:56 a.m. and found a crowd of about 40 people milling about and an unconscious man on the ground bleeding from his face, Cruz said.

The injured man was being tended to by several bystanders and a Hoboken police officer. Police dispersing the crowd were told that Castro and Nunfio, both of Jersey City, were the two who knocked out the man.

Castro and Nunfio were still at the scene and Castro told officers that he struck the victim. Witnesses said Castro and Nunfio struck the victim several times, knocking him unconscious and then continued to hit the victim while he lay prone on the ground, Cruz said.

The two were arrested and Castro was released on a summons, while Nunfio was taken to Hudson County jail in Kearny, Cruz said. Both appeared in Criminal Justice Reform Court on Monday.

The victim suffered serious head trauma and remains under observation at the Jersey City Medical Center.