Fumigant chemical lost overboard from a ship about 200km offshore from Opotiki last week might wash ashore in the Gisborne or Bay of Plenty districts and should not be touched.
The metal canisters contained a dangerous fumigant, said Bay of Plenty Regional Council manager maritime operations, Reuben Fraser.
The MV Gladiator was en route from Napier to China in rough seas on Wednesday night when a box containing 14 flasks of aluminium phosphide (ALP) washed overboard. Each flask contains chemical used for treating wood products, weighs 1.5kg and has a red and white label with the name Genfume AP and poison warnings.
There was only a small chance that the canisters had entered the Bay of Plenty's waters, as prevailing currents and winds were likely to take them further out to sea, he said. However, residents needed to be aware that they could wash up on the beaches.
Gisborne District Council spokeswoman Toni Lexmond said there was only a small chance the canisters would appear in the district but people should be aware.