Police in New Jersey are searching for a gunman after multiple shots were fired inside a shopping centre.

Bergen County spokeswoman Jeanne Baratta told the Associated Press that authorities believe the suspect is still inside the Garden State Plaza Mall in Paramus.

She said Swat teams are concentrating their search in the north-east corner of the 200,000 sq metre mall, near the Nordstrom department store.

Ms Baratta said a call was received saying shots had been fired at the facility shortly before the mall's 9.30pm closing time last night. No injuries have been reported.

Paramus Police chief Kenneth Ehrenberg said the suspect was dressed in black and was wearing what is believed to be a motorcycle helmet. A weapon has not yet been recovered.

Witnesses said the sound of gunfire sent customers and employees rushing for the exits and hiding places.

Ms Baratta said authorities had found one bullet casing.

Hundreds of law enforcement officers converged on the mall, which was put on lockdown. New Jersey State Police landed a helicopter in the car park of one of the state's largest and most popular shopping centres.

Ms Baratta said Swat teams and police with dogs were going through the mall and working to evacuate anyone still inside. As of early today, authorities believed there were still people in the mall, she said.

At around 1am Nordstrom tweeted that everyone in its store had been released safely. "Our thoughts are with those still involved. We hope for a swift resolution," the tweet said.

The mall later tweeted its thanks to law enforcement, saying: "We are sincerely grateful for the rapid response from law enforcement." It added that Garden State Plaza Mall would be closed today.

Nick Woods was working in the Lego store when a woman ran by shouting that there was a shooting.

Mr Woods said his supervisor locked them in a back room, along with a woman, a man and a child. When they finally peeped out two hours later, he said they saw police officers standing outside and he called the police emergency dispatcher to ask that the officers be told they were coming out.

He said the emergency operator told him she could not contact individual police officers and that he should walk out with his hands in the air.

"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," Mr Woods said. "It was one of the scariest experiences of my life."

Jessica Stigliano, 21, of Richfield, New Jersey, told the AP that she was sitting in the mall's food court when she saw people running and yelling "shots were fired",

She said she also began running and at the time she was thinking: "Not many people run for their life, but that's what I'm doing right now."

Carlos Sinde, 36, of Astoria, Queens, said he was at the mall to see the 9.20pm showing of the film Gravity when the fire alarms went off and the movie stopped.

He said he walked into the mall where someone was saying "I think there was a shooting" but he did not take them seriously. Then, security guards ran up, urging customers to leave. He said one female security guard was crying.

"Once the security guards started telling us what was going on, that's when there was hysteria," he said.

Early today, families were being escorted by police to a Chili's restaurant on the outskirts of the mall area to be reunited with others who had been in the shopping centre for hours.

Althea Brown, 26, of Paterson, told NorthJersey.com she was in a clothing store when she saw a man walk by and then heard three shots followed by two more. She said he appeared to be wearing body armor and was wearing a helmet with the visor pulled up.

Several frightened customers sent tweets saying they were escorted from the mall by armed state troopers. One woman wrote that she ran from the mall "screaming".

The mall, which has more than 270 stores, is located in Bergen County, about 24km north-west of Manhattan.