The discovery of a potentially lethal toxin has led to an urgent recall of mussels from a Tasmanian shellfish farm.

A public health alert has been issued after routine testing found unsafe levels of paralytic shellfish toxin in mussels from Spring Bay Seafoods.

The likely cause is a naturally occurring algal bloom near Maria Island on the state's east coast.

If so, it will be the first time in Australia this type of algae has been found to be toxic.

Public Health Director Roscoe Taylor has urged people not to eat farmed or wild shellfish from the affected region.

He says cooking or freezing does not destroy the toxin.

"We routinely advise the public never to consume wild shellfish because we're not certain about the water quality in the areas that they're growing," he said.

"But now that we know about the toxin I would re-double that warning."

There have been no reports of illness so far but the toxin can be deadly, especially in children.

"It can cause tingling in the mouth, weakness and tingling in the arms and legs, a progressive weakness sometimes, associated with nausea, and ultimately, if sufficient toxin is consumed, it can be fatal," Dr Taylor said.

The Spring Bay Seafoods farm has been shut down.

Shellfish farms in Little Swanport, Georges Bay and Ansons Bay have also been closed as a precaution.

The recalled mussels have been distributed in Tasmania, Victoria, New South Wales, South Australia, Queensland and the ACT, along with several Asian countries including Japan.

The affected products are Spring Bay Live Blue Mussels with use by dates between October 22 and November 10, and Coles Cooked Tasmanian Mussels with use by date November 12.

Wes Ford from The Department of Primary Industries says it is too early to calculate the cost to the industry.

"There's also the issue associated with branding and one of the really important aspects to remember is that this is just part of the process of shellfish farming, it's very precautionary," he said.

Primary Industries Minister Bryan Green says it is devastating for Spring Bay Seafoods and its workforce.

"Tasmania has an excellent reputation for high-quality, safe shellfish and it is hoped this is a short term event and will have no lasting impacts," he said.

Authorities are continuing testing but say it is likely to take weeks for the bloom to clear.

Anyone who experiences symptoms after eating seafood from or near the affected area is urged to seek immediate medical attention.

More information can be found on the Food Standards Australia New Zealand website.