The yacht can take up to 64 passengers
Pirates have boarded a luxury French yacht off the coast of Somalia, taking all its 30 crew hostage, French officials and the ship's owners say.
They say the Ponant was seized in the Gulf of Aden and had no passengers on board at the time.
France's government said it had launched a piracy alert plan, mobilising all resources in the area.
Somali coastal waters are among the most hazardous in the world, despite the presence of US navy patrols there.
Last year, pirates seized more than 25 ships in the area.
'Act of piracy'
The Ponant - an 850-tonne three-masted yacht - was sailing back to the Mediterranean from the Seychelles when it was seized, officials said.
"As far as we know, no shots have been fired," French military spokesman Christophe Prazuck was quoted as saying by the AFP news agency.
The yacht's owners - the shipping group CMA CGM - confirmed that one of its vessels had been seized.
The company said that the majority of the crew were French nationals.
French Prime Minister Francois Fillon later on Friday described the incident as "a blatant act of piracy".
"The defence and foreign ministries are mobilised to act as quickly as possible.
"I hope in the coming minutes or hours to try to win the freedom of these hostages," Mr Fillon said.
French and allied forces stationed in the area were put under alert.
France has troops in nearby Djibouti and also participates in a multinational naval force that patrols this part of the Indian Ocean.
The hijacked yacht can take up to 64 passengers and is designed for cruising in some style.
It has four decks, two restaurants and also indoor and outdoor luxury lounges.