AJACCIO - A DARING heist saw an armed gang target a luxury yacht off a Mediterranean island with German financiers on board robbed of a large cash sum, officials said on Monday.

Masked gunmen stormed aboard the yacht off the French island of Corsica, overpowered crew and guests and made off with 138,000 euros (S$289,272) from its safe.

It was the first time such a security breach has occurred in French waters, officials said.

Speaking French with a Corsican accent the men, armed with rifles and handguns, boarded the 55-metre Cayman Islands-registered Tiara just before midnight on Sunday and quickly overwhelmed the 10 crew members and nine German passengers, police said.

'The operation only took a few minutes and, apart from the threat of their weapons, the robbers did not commit violence against the ship's occupants,' according to a source close to the investigation.

'Nor were they interested in the wallets or the jewels' of those on board the Sardinia-bound yacht, the source added.

Once they had grabbed the money from the safe they made off on the same rubber dinghy they had arrived in.

Tiara was moored off Porto Vecchio in the south of the island at the time of the robbery. In 1997, two English tourists were robbed at sea, but the manner of this raid was completely unique, police said.

The prosecutors' office in the Corsican capital Ajaccio has opened an inquiry which is leaning on police from further south, along with those from Porto-Vecchio.

Ajaccio prosecutor Jose Thorel confirmed the Tiara was carrying 138,000 euros in its safe.

As of late Monday, the investigators' search for the assailants' dinghy was ongoing, while they were still questioning the passengers and crew.

Those renting the yacht for the month - at a cost of 180,000 euros a week, according to prices listed on the Internet by its charter company - were wealthy members of the German financial world who preferred to remain anonymous, the investigative source said.

'They aren't known personalities but people with a solid financial foundation,' was all the official would say.

The art-deco styled Tiara has five cabins and at least one marble bathroom and can sleep up to a dozen passengers. Its rear deck is large enough to fit a helicopter.

It is a well-known sea fixture for Corsicans who watch it pass by regularly. -- AFP