Police have confirmed they are now reviewing a stunt that was pitched as a $100,000 money drop in downtown Auckland - but which turned out to be mostly fake cash.

The Reserve Bank has also issued a warning that it is illegal to publish anything resembling a genuine banknote after fake $5 dollar notes rained down on people clambering for what they thought was cash.

Acting Auckland Central Area Commander Inspector Scott Gemmell confirmed to the Herald today: "Police will be reviewing this incident and will be making follow up inquiries with the event organisers."

Safety Warehouse is under siege from furious members of the public who attended Saturday's event in Aotea Square. The company pledged to giveaway $100,000 in cash but the crowd turned ugly when many realised pretend $5 notes - which could be used as a discount - were being distributed.

The fake notes were designed to look like real currency but with the photo of Sir Edmund Hillary replaced.

A spokesman for the Reserve Bank has confirmed it is a criminal offence to publish anything resembling real banknotes.

"(We) are unable to comment directly on the legality of any reproduction or imitation currency used in an Auckland marketing event on Saturday, 5 December, due to an ongoing police review.

"However, it is reminding event organisers and the marketing industry that publishing anything resembling a genuine banknote or coin - or which could be mistaken for the real thing - may breach the law."

More than 1000 people gathered in the square at noon that day after the company promoted plans to drop $100,000 from the sky.

One disgusted attendee has started a Change.org petition demanding people with vouchers be paid real money and planned a police complaint, saying vouchers resembling $5 notes were scattered to the crowd in Aotea Square.

Outraged members of the public, including Levin's John Murphy, called the event a waste of time, and claimed many attendees were from impoverished backgrounds who felt duped.

The under-fire boss of Safety Warehouse, Andrew Thorn, has defended the controversial giveaway at Aotea Square, saying it has been unfairly characterised as an event with "fake money".