Five teenagers are in custody after shoppers reported the dramatic sight of a group of males carrying firearms through a Westfield in northern Sydney.

Police from North Shore Police Area Command were called to the shopping centre in Chatswood at about 6.30pm. They arrested an 18-year-old man and four teenage boys aged 17 at about 6.40pm outside a supermarket and seized several replica guns.

It is unclear whether the men were threatening shoppers, but police handcuffed them on the floor of the centre.

Three were taken to Chatswood Police Station, and two were taken to North Sydney Police Station, where they are assisting with inquiries.

Witnesses told Seven News they saw police run into the shopping centre and scream at the boys to get down on the ground, with some drawing their guns.

A worker at the nearby Coles made the decision to put the store’s roller-door down to lock employees and shoppers inside.

Security then ran around to other stores to tell them to do the same thing.

Another witness, Emily Bruce, said she was terrified while the incident was unfolding. “I was about to pay for a foot massage out the front of Tailou Health when police rushed past me yelling ‘get down’ and ‘drop the gun’,” she told Nine News.

A shop staff member claimed some confused shoppers were screaming about a terrorist attack. “The other shoppers were screaming terrorist attack, so we believed that was what was happening. We backed up to a distance of safety and tried to figure out what was going on,” the staff member said. “(Police) were on the scene very quickly, around 10 to 15 of them from every direction.”

No one was physically injured during the incident.

As inquiries continue, anyone with information is urged to come forward.