Police in the semi-autonomous Indian Ocean island of Zanzibar on Wednesday said they had seized a 40-foot (12-metre) container hiding an estimated several tonnes' worth of ivory.
The seizure comes as authorities in Tanzania crack down on poaching amid a surge of killings of elephant and rhino in the east African nation.
"This is unacceptable, we must end this problem," said Tanzanian Natural Resources and Tourism Minister Khamis Kagasheki, who travelled to Zanzibar after the seizure.
"This is serious, let us join forces to save our natural resources," said the minister as police officers searched the container.
It was not clear where the container was destined for.
Police estimated that several tonnes of ivory were stashed in the container but said they would only be able to give the exact weight of the tusks, as well as the origin and destination of the ivory, once they finished unpacking it.
Kagasheki warned that if authorities were unable to find the owner, the agents who cleared the container on its arrival in Zanzibar's main port would be held accountable.
"How did ivory manage to be transported to Zanzibar for reshipment?" Kagasheki said.
Zanzibar police chief Mussa Ali Mussa said two workers from a local clearing agent, which he refused to name, had been taken into custody.
In August 2011, at the same port, police seized 1,041 elephant tusks hidden in a shipment of anchovies heading for Malaysia.
The consignment had arrived from the Tanzanian economic capital Dar es Salaam.
The lucrative Asian black market for rhino horn, used in traditional medicine, and ivory has driven a boom in poaching across Africa.
Last week President Jakaya Kikwete told parliament that a controversial anti-poaching operation that allegedly used a shoot-to-kill policy would continue in a bid to stamp out poaching.
Earlier this month three Chinese nationals were charged in mainland Tanzania for possessing 706 tusks from poached elephants. The trio face a maximum sentence of 20 years if found guilty.
Explore further: Fears for pink iguanas as Galapagos volcano erupts