UPDATE: Police are urging beach goers to avoid handling any silver canisters washed up on the local beaches and to immediately call Triple Zero (000).
The canisters, similar to the one pictured, are about 30cm high and 15cm in diameter and contain aluminium phosphide, which could be fatal if inhaled or ingested.
A canister was located on Lady Elliot Island on December 10.
A second canister was located by a Rules Beach resident two weeks ago but was only reported to police on Saturday, and a third canister was located at Deep Creek, south of Gladstone, on Sunday morning.
Gladstone District Officer Superintendent Glenn Kachel said the canisters were believed to be from the same batch that has been washing up intermittently along the North Queensland coastline, from Cooktown to Ayr, since about mid-October.
"The canisters contain a toxic substance. For safety's sake, should anyone find one, I urge them to immediately report it by calling triple zero. Do not inspect the contents, open the canister or transport it."
Aluminium phosphide is a colourless, flammable and toxic gas. Mild exposure by inhalation can cause a feeling of sickness, ringing in the ears, fatigue, nausea and pressure in the chest which is relieved by getting away from the gas and getting fresh air.
UPDATE: Early reports indicate a second canister of aluminum phosphide washed up on Rules Beach.
Police have no further details at this stage.
Saturday: The Baffle Creek Post Office received its most unusual parcel when a canister of aluminum phosphide washed up on the beach.
The post office owner came across the harmful substance at Rules Beach two weeks ago.
Emergency services were informed on Saturday and Gladstone fire crews were sent out to dispose of the canister.