Potentially-deadly B.C. shellfish taken from an area of northern Vancouver Island that is closed to harvesting are being sold online, according to Fisheries and Oceans Canada (DFO).

Fisheries officer Mandy Norrish said that butter clams, and possibly other shellfish, that were advertised for sale through a Facebook page may have come from an area closed due to red tide.

"The Port Hardy DFO office was alerted to some products for sale on the Facebook page 'Port Hardy Buy, Sell and Trade,'" Norrish said.

The post advertised butter clams, and possibly other shellfish, being sold by a person in Port Hardy.

The DFO said the shellfish could be contaminated with marine toxins that cause paralytic shellfish poisoning, and cooking doesn't destroy the toxins.

The contraband product was being sold in 40-kilogram sacks that do not have inspection tags attached to them, Norrish said.

DFO regulations state that "all bivalve shellfish sold in B.C. must come from open shellfish harvesting areas and from sources that pass federal inspection."

Norrish says consumers can protect themselves by asking to see fishing licences, checking for inspection tags that should be attached to shellfish products sold and requesting receipts from vendors.

"If you're ever in doubt, ask to see someone's licence and usually your first red flag is when you ask for a receipt and someone says 'no,' then don't buy it," she said.

An investigation is underway and the DFO is asking anyone with information to call its 24-hour report line.

So far, there have been no reported cases of sickness or death.

Officials aren't saying whether a similar warning and investigation last December is connected. No charges have been laid in either case.

With files from the CBC's Lisa Cordasco