Those behind a Sydney fireworks display where nine people were injured after a cracker ricocheted into the crowd say it appears a manufacturing error was to blame.

SafeWork NSW is investigating the incident at the family Christmas carol event on Sydney’s northern beaches, from where three children were taken to hospital after the frightening malfunction.

Emergency services were called to Allambie Heights Oval at 9.30pm on Sunday after the fireworks display went horribly wrong.

Police say one of the fireworks shot into the crowd and struck some of the revellers.

Mark Bryant, who was among the crowd, said it was frightening and “kids were running everywhere”.

“It was pretty scary stuff,” he told ABC TV on Monday.

An 11-year-old boy was taken to Royal North Shore Hospital then transferred to the Children’s Hospital at Westmead for treatment of burns and a chest injury.

An eight-year-old girl was taken to Northern Beaches Hospital with a burned wrist and has since been released. A 12-year-old boy was taken to hospital for treatment to minor burns and has also since been released.

Six other people were treated at the scene by NSW Rural Fire Service for minor injuries and left before paramedics and police arrived.

Howard & Sons, which describes itself as “a globally renowned fireworks and special effects company”, was responsible for the display.

On Monday, Christian Howard said initial investigations indicated there was a manufacturing problem with the firework, rather than human error.

“We haven’t had a problem with this product in the past but there have been Roman candles in the past that have malfunctioned,” he told ABC TV.

Police have established a crime scene at the oval and SafeWork NSW is investigating.

“As inquiries are continuing no further comment is available at this time,” a statement from SafeWork NSW said.

-with AAP