Shoppers at Riccarton Mall were shocked when a man on a bike pulled a taser on members of the public.

Witness Brad says the man was riding a bike through the inside of Riccarton Mall when he grabbed a USB speaker from a kiosk.

"Members of the public knocked him off his bike and he produced a taser and tried to taser two or three people."

He says bystanders managed to pin the offender to the floor, but when security guard told them to let him go, he ran out of the mall and down Riccarton road.

He left his bike and the speaker behind.