The drugs were stored in 797 medium-sized containers wrapped in brown tape and seized from a vacant house under construction in Namaka in Nadi, police said in a statement on Monday.
They have not put a street value on the haul but, based on the NZ drug trend survey, it could be priced in the hundreds of millions of dollars if it landed in New Zealand.
An investigation is continuing and no further details on the people involved have been released.
RNZ Pacific has contacted Fiji police for more information.
In a statement, Acting Police Commissioner Juki Fong Chew said the "fight against drugs" continues in the form of "consistent raids" with "more drugs being seized".
"This is one of the biggest seizures ever and this shows that we are on top of things.
"The white powder seized was over three tonnes and it was stored in 797 medium-size containers. Our fight against drugs continue and we are out there trying to make our country free from drugs."
Engagements with the organisation's external partners continues as part of its fight against illicit drugs, he said.
Last year, the government made the admission it was losing the fight against the sale and consumption of illegal drugs.
Attorney-General Siromi Turaga was pleading with traditional leaders to work with police to address the drug problem, local media reported.
Turaga said the use of methamphetamine, which is known by the street name "ice", had become widespread and affecting people's lives.
He warned the illegal substance has flooded the community "and even school children are selling" it.
Children needed to be protected, he believed, as concerns were being raised about them being used to peddle and distribute drugs.
According to Drug Free World Fiji founder Kalesi Volatabu, one in three children on the streets were "highly likely" users of meth and other hard drugs.
