A Gottfried Lindauer painting stolen in a brazen ram raid is apparently being auctioned on the dark web for nearly $1 million, but the gallery it was stolen from has no doubt the sale is a scam.

The seller, who goes by the name Diabolo, said the 133-year-old portrait of Chief Ngatai-Raure, which is worth between $350,000 and $450,000, is genuine.

"Here you can bid on an (sic) TOP SECRET original Painting from Bohemian painter Gottfried Lindauer that was stolen in New Zealand, Auckland, 2017," the listing said according to Wired.

It is running as a bitcoin auction, as well as having a "buy now" price of 35.1129 bitcoin - about NZD $417,000.

The painting, along with one of Chieftainess Ngatai-Raure, was stolen from the International Art Centre in Parnell on April 1. CCTV footage showed a stolen ute backed through a gallery window and two thieves made off with the portraits.

International Art Centre director Richard Thomson told NZ Newswire he has no doubt the dark web auction is bogus.

"I was alerted to this two weeks ago and our people had a close look (on screen) and it's obviously photoshopped, which is easy to do in this day and age," he said.

"You'd be mad to consider buying it."

As insurance had paid out on the theft, Mr Thomson said he is "emotionally detached" from the portraits, but would always be curious to see if they re- surfaced one day.

He had a theory about the auction.

"I suggest it might be a decoy - this auction could be a complete distraction for it to be sold somewhere else."

Detective Inspector Scott Beard said police were continuing to investigate the theft of the paintings.

"We are aware of the listing but as our investigation is ongoing, we are unable to discuss specific details," he said in a statement.

The dark web, which requires specialist skills and tools to access, is traditionally used for illegal activity, such as the sale of drugs and weapons.

- NZ Newswire