A 20-year-old man suspected of firing a gun and forcing the closure of a large shopping mall in the US state of New Jersey has been found dead of a self-inflicted wound, local authorities say.

John Molinelli, Bergen county prosecutor, said the body of Richard Shoop, of Teaneck, New Jersey, was found in a back area of the Garden State Plaza shopping centre in Paramus on Monday night.

The shopping centre, about 35km southwest of Manhattan, was evacuated shortly before closing time on Monday night after multiple shots were heard.

Witnesses reported seeing a man dressed in black and wearing a black helmet, and hearing up to five shots just after 9pm.

Molinelli said Shoop killed himself with the same weapon he fired at the mall and that a note was found. There were no other injuries.

Kenneth Ehrenberg, Paramus police chief, said Shoop did not work at the mall, and police were still searching for a possible motive for the shooting.

Hundreds of law enforcement officers, including SWAT teams with K-9 units, converged on the 2.2 million-square-foot mall, searching for the shooter and evacuating anyone who was still inside.

Authorities say they found one bullet casing.

Nick Woods, an employee of the mall's Lego store, said his supervisor locked him in a back room, along with a man and a child who ran into the store after the shots were heard.

They emerged from hiding two hours later to see police officers standing outside.

"I had to go out of the store shouting at the officers with my hands up, and they turned and pointed their guns at me," Woods said. "It was one of the scariest experiences of my life."

Source: Agencies