Police say they believe there is a good chance authorities will make arrests over a record cocaine seizure in the Pacific Ocean.

More than three tonnes of the drug were found floating in international waters by the Defence Force last week.

Operation Hydros - a joint mission by police, Customs and the Defence Force - seized 81 bales of the drug, totalling 3.2 tonnes, with an estimated street value of half a billion dollars.

Police Commissioner Andrew Coster told Morning Report the amount was enough to supply the New Zealand market for 30 years or the Australian market for one year.

"I think we've got a good chance of tracking down offenders for this and obviously that's an ongoing investigation, but even if we don't, the social harm prevented by holding that quantity out of our communities is significant."

Police estimate $9 billion of harm has been prevented by removing the drug, says Coster.

There's not a large market for cocaine in New Zealand, but the drug is just as harmful as meth or heroin, he says.

Methamphetamine is New Zealand's biggest drug problem and Coster says the cocaine was not likely to have been destined for this country, although some may have got here had the police not intercepted it.

"This is probably more significant for our contribution to the international environment, particularly in terms of Australia.

"We often will get benefit from Australian investigations that mitigate the harm from methamphetamine and so on here, so a bit of swings and roundabouts but a great result for the region."

-RNZ.