A jar of Manuka Honey, which sells for $9.99 at the German supermarket chain, has been spotted inside a locked plastic case at an Aldi store in Braybrook.

The highly sought-after honey is made by bees that feed on manuka bushes - Leptospermum scoparium - growing in the wild, and is cultivated on a large scale in New Zealand, but also in Australia.

The rare plants are often so inaccessible honey farmers have been known to seek them out with helicopters and drop hives nearby.

A top-of-the-line jar of the sticky stuff can cost $120 for 500 grams, but most stores across the state sell top-grade versions of the product for about $40 per jar.

There is growing demand for the honey, which is highly valued for its anti-bacterial properties and is also used in the pharmaceutical industry.

An Aldi Australia spokeswoman said the Braybrook plastic box was one of many ways the supermarket chain was trying to deter theft.

"We have a number of security measures in place across our stores to help minimise theft and loss to our businesses," she said.

Other items sold at Aldi, including razors, batteries and mobile phones are already under lock and key, she said.

Earlier this year, supermarket giant Coles announced it was testing out a 12-item limit for self-service checkouts in some stores to combat increasing theft.

The supermarkets estimate that up to a third of self-serve customers deliberately swipe the barcode of a cheaper item when putting items through a checkout - or don't swipe at all.

A Kmart store in Reservoir also made headlines earlier this year when it opted to lock Cadbury chocolate blocks in security cases.