Hold on - that elite Merc car order is going at a snail's pace

In the past, invasive marmorated stink bugs have stopped shipments of cars into Australia, but now it's European snails.

The Heath snail poses a huge risk to many Australian crops including lupins, clover, wheat, barley and fruit trees.

The snails (Xerolenta obvia) were found in luxury Mercedes cars at Port Kembla, and at other ports.

The Department of Agriculture has already detected 30 cases of snails in imported to Australian ports of Fremantle, Melbourne, Port Kembla and Brisbane.

The Department announced it had directed a shipment of cars from Europe to leave Australia after snails were detected on board.

Agriculture Minister Bridget McKenzie said four other vessels carrying the cars had been banned from unloading "because protecting Australia's biosecurity integrity was critically important".

"Whether you're a passenger coming through the airport or a multinational company importing bulk goods the same stringent standards apply," Mrs McKenzie said.

"Based on the risk we identified, my department has refused permission for a further four shipments of potentially contaminated vehicles to offload in Australia.

"The importer has been working with my department to manage the biosecurity risk and I thank them for their cooperation. This followed the detection of an infestation of Heath snails (Xerolenta obvia) on vehicle shipments to four states involving about 900 cars.

"These hitchhiker pests threaten Australia's environment and agriculture industries because they feed on a wide variety of plants including crops like alfalfa, lupins, clover, wheat, barley and fruit trees as well as native plants and weeds.

"We take threats to Australia's animal and plant health very seriously as our pest and disease free status underpins our export proposition to the world - we're clean, green and safe.

"More than 30 snails have been found by biosecurity officers in vehicle shipments to date on cars imported to Fremantle, Melbourne, Port Kembla and Brisbane."

"The person in charge of the goods has been given a direction to export the vehicles and vessels on the water have been informed that they cannot unload here.

"The importer has been working closely with the department to manage the biosecurity risk after the department considered treatment options to manage the risk onshore and determined the most appropriate action was to export the vehicles from Australia."

The department said Heath snails were a pest in south-eastern Europe and have established localised populations in Canada and the USA.