An octopus the size of a rugby ball made an audacious escape through a narrow pipe at New Zealand's National Aquarium, reports said, with the "great escape artist" returning to the ocean.

"Inky" the male octopus, given to the Napier aquarium two years ago after being rescued from a crayfish pot, made a dash for freedom by slipping through a small gap in his enclosure, sliding across a wet floor and squeezing through a 150-millimetre-diameter pipe, Fairfax New Zealand reported on Tuesday.

"Octopus are really intelligent animals, very inquisitive, and they also tend to explore whenever they get the chance," aquarium manager Rob Yarrell told MediaWorks' Newshub on Wednesday.

"Giving him just a little gap was enough for him to get out and we noticed the wet trail across to one of our drains."

The reports did not state when Inky made his getaway, reportedly the first-ever at the aquarium.

"They are great escape artists," Yarrell told the New Zealand Herald, saying staff would be closely watching the remaining octopus in the enclosure.

While Inky was the size of a rugby ball he could stretch to extremes and squeeze through tiny spaces, Yarrell said.

"As long as its mouth can fit," he told Fairfax. "Their bodies are squishy but they have a beak, like a parrot."