Police in French Polynesia have seized almost $US50 million worth of methamphetamine on a cruise ship from the United States.

A 27-year-old Tahitian passenger has been arrested after the discovery of 21 kilograms of the drug in his luggage.

The authorities say the man had wanted to offload a suitcase when the ship, the MS Zuiderdam was in port in Uturoa on Raiatea.

More than four kilograms of the drug were found in the suitcase.

A subsequent search of his cabin turned up a further 15 kilograms of methamphetamine in other luggage.

The passenger, who has been transferred to Papeete for further questioning, risks a jail term of up to ten years.