Australian police seized 300 kilograms (650 pounds) of cocaine from a luxury yacht and charged four Spaniards with drug trafficking in one of the country's biggest ever busts, officials said Monday.

The drugs, worth some Aus$78 million (US$80 million), were found in the hull of the yacht, which left Vanuatu in the Pacific on October 14 under close watch after intelligence linked it to a global crime syndicate, police said.

"It is believed to be the fifth largest cocaine seizure in Australian history," police said.

"It is also the second significant cocaine seizure on a yacht in just over 12 months."

Two Spanish citizens crewing the yacht, a man, 35, and a woman, 37, were arrested along with two other Spaniards -- men aged 38 and 39 -- when the boat docked in northern Bundaberg to drop off 100 kilograms of cocaine.

"Police will allege that (the) two other Spanish nationals... travelled from the Gold Coast to Bundaberg on Friday, 11 November to meet the boat," police said.

More than Aus$3 million in cash was seized in searches related to the bust, and the four Spaniards were to face court later Monday on charges of commercial drug importation, which carry a maximum penalty of life imprisonment.

Police said they had not ruled out making more arrests.

Justice Minister Brendan O'Connor said it was the culmination of several months of surveillance and involved significant maritime and aviation operations, including collaboration with Vanuatu authorities.

"Australia's law enforcement agencies are skilled and well-resourced to protect us from the scourge that drug syndicates try to force upon our communities," O'Connor said.

"This government will not tolerate our country becoming a target of drug syndicates and international organised crime."

Cocaine seizures more than doubled last year, up 103 percent to 796 kilograms, under a crackdown on organised crime.