The Senegalese authorities have found an empty sailing boat with 1.2 metric tons of cocaine on board, they say.
Poor West African states are seen as a new hub for the drugs trade
The boat was found near the Atlantic Ocean resort of Mbour, with the drugs divided into 50 bags of 24kg each - Senegal's biggest cocaine seizure.
Police say they found plane tickets from Brazil to Guinea-Bissau, now seen as a major drug-trafficking centre.
In Bissau, magistrates have condemned an ex-prime minister's statement that he ordered the destruction of cocaine.
The cocaine found in Senegal was worth some $100m on the streets of Western Europe.
Experts say that West Africa's poor, coastal countries are increasingly becoming a major hub in the trafficking of cocaine from Latin America to Europe.
There have also been large cocaine seizures recently in Ghana and Sierra Leone.
Former Guinea-Bissau Prime Minister Aristides Gomes said on Thursday that he had said the drugs should be burnt - following speculation that the haul had disappeared.
"Under pressure from me and my direct order the 674 kg of cocaine were burned in my absence," he said.
"Anyone who doubts that can take the affair to the courts."
But the Bissau magistrates' union says that the correct procedures for destroying the drugs were not followed.
It says it is concerned about the government's alleged role in the drugs' trade.
The cocaine was seized last September and was stored in a treasury vault before going missing.
Seven top officials were arrested over the affair but have not been charged.
Another 635kg of cocaine was found in Bissau in April but the United Nations drugs agency reports that traffickers escaped with almost two tons of the drugs, which had been flown into a military airstrip.
At the time, UN Office on Drugs and Crime head Antonio Maria Costa said he feared Guinea-Bissau could become a "narco-state" unless donors did more to make the police force more effective.
"It is regrettable that the rest of the consignment was not intercepted but hardly surprising as the police are woefully ill-equipped and often do not even have enough gasoline to operate their vehicles," he said.