"At that stage no one knew the flood was coming," he said.
Sally Patrick, Wanganui District Council community and cultural manager, said the Quay Gallery upstairs of the i-Site, was as secure as they could make it.
"But we will be reviewing our display policy and meanwhile we've removed everything on display there," she said.
The value of the items has been circulated to auction houses and customs. The property is covered by insurance.
Mr Anderson said he did not think the works could find their way overseas and were certainly not saleable.
"People would know instantly the work had been stolen. It's very distinctive art work."
Ms Patrick said there was "huge trust" between the gallery and the artists and that was why they were anxious to move quickly to recover the stolen works.
"We want them back," she said.
The Sarjeant staff had recently moved out of their significantly earthquake-prone building on Queens Park into temporary premises on Taupo Quay, shifting 8000 artworks in the process. And now, along with other businesses along Taupo Quay, their temporary gallery has been flooded.
"A serious flood was obviously a risk we planned for and our collections of national significance are housed away from the threat of flooding and are very safe," he said.
But he said the theft of artwork from an otherwise secure display at the i-Site, was unexpected.
"After five years of business-as-usual and about 50,000 visitors to the i-Site Gallery, such an event is completely unprecedented.
"My team are devastated, particularly for Rick Rudd, who has for so long supported the gallery and whose work forms a major part of our ceramic collection," Mr Anderson says.
He said security procedures had been more than sufficient up until now but in light of this theft they will be reviewed.
"We want to see this matter resolved as soon as possible, and give reassurance to our lenders that our stewardship processes are very sound."