Creators of the Lewis Road Creamery chocolate milk say its popularity has gone beyond their wildest expectations.

Security guards have been put in place at some Auckland supermarkets to monitor the milk as demand spins out of control.

Since it went on sale three weeks ago, customers have been queuing up for new deliveries, which sometimes go in a matter of minutes.

Lewis Road Creamery founder Peter Cullinane says they're producing at full capacity but can't keep up with the demand.

"I think it's going to be in reasonably scarce supply for quite a long time.

"It's a wonderful problem to have, I suppose, but not actually ideal for our retailers who really don't like letting their customers down."