International Art Centre director Richard Thomson says the thieves may not have known the value of the treasured Charles Goldie painting when they took it.
The theft of the painting from a Hamilton property this week has outraged the country's art buffs.
Sleep 'tis a Gentle Thing was taken along with other valuable artworks and antiques between December 27 and January 3.
Goldie produced several versions of the painting, which depicts a sleeping chief Hori Pakai. One was sold at the International Art Centre in 2009, fetching $454,000.
Having reviewed a police photo of the stolen work, centre director Richard Thomson believes it could be the same one.
Thomson told Morning Report the theft was upsetting for the community and he has urged whoever was responsible for the theft to return it as if they try to sell it, they'll be caught.
"They've grabbed it and they taken a major piece of New Zealand's art history and they need to return it," he said.
"It's sad that someone's taken it, but it doesn't necessarily sound like they know what it is, but what else has been taken doesn't look that interesting...
"It seems odd that they've taken that and then another painting of no value, so it doesn't seem to me that they know the significance of it... it seems an opportunist theft, or they've targeted that and grabbed what else they could at the time."
He said the painting had both monetary and historical value, estimating this particular Goldie work could reach well over a $1 million.
"A painting like that we've sold similar for $1.4 million at auction, so I would say the value is between $800,000 and $1.2 million for that particular example, because its a really good example.
"I have sold one similar again in 2008 at $454,000 at auction, but the market has moved considerably since then... It's unusual now for a Goldie to sell below half a million. But this is a classic Goldie, a very good example."
The work was painted between 1933 and 1938, making it a late example, when the artist was in his 60s.
"It is a significant piece because really good works were done at that time."
The thieves, Thomson said, would be unwise to attempt to sell the painting and it was in their best interests to find a way of returning it.
"It's absolutely no value to them whatsoever. If they think they can sell it on the market or international market, they just can't. It's hot property and as soon as someone spots it, it will be reported. So it would be foolish to do anything with it. Take it into your local police station, call us, or call the radio, take it back."
Other items taken from the house included a Koch & Bergfeld cutlery set. Police are appealing for information, including sightings of the items.
The International Art Centre was also subject to a major theft back in 2017 when two paintings by Goldie's contemporary Gottfried Lindauer were taken in a ram raid robbery.