The chemical generates toxic phosphine gas in contact with air or moisture and could burst into flame.
Anyone finding the canisters should not open them and report them to the Bay of Plenty Regional Council's pollution hotline 0800 884 883.
Mr Fraser said it was a highly-toxic substance, so people should not try to pick it up or open it.
"With school holidays this week, it's vital that parents warn children playing on the beach not to touch the canisters, since they are small enough to attract children's interest."
People exposed to even low levels of the chemical will feel ill and it can also cause ringing in the ears, fatigue, nausea and pressure in the chest. High concentrations can be fatal.
The chemical can irritate skin and eyes and it is toxic if swallowed.
Mr Fraser said the regional council was notified only yesterday morning about the loss of the canisters.
The box of canisters had been placed in the ship's storeroom but the door was left open when the ship sailed. During rough weather, water washed into the storeroom, washing the flasks and other items into the sea.
"ALP is safe in the flask and is very difficult to open. If the flasks wash up we will collect and dispose of them," he said.
- Gisborne Herald