Luxury cruise ships were employed by alleged drug mules to smuggle cannabis and cocaine across the Atlantic Ocean alongside elderly holidaymakers.

Eight women and 23 men recruited in the French city of Nice are accused of trafficking drugs while on intercontinental trips chartered by Costa Cruises over a period of two years.

A French court heard that the defendants boarded the extravagant cruiseliner in Italy, stopping off to pick up cannabis in Morocco before trading it for cocaine in Brazil, which was returned to Europe in exchange for money.

The youthful French-speaking mules caught the attention of crew members who were used to catering for elderly Italian couples at retirement age, according to The Times.

"They wondered what these young people were doing going on cruises with old people when they were not there to accompany their grandmothers," Patrick Ardid, the chief judge, said.

Cruise ships chartered by Costa are luxury vessels featuring swimming pools, cinemas, showrooms and several bars and restaurants.

The accused, largely from Les Moulins in Nice, also drew attention because they avoided each other while on board the ships but took taxis together upon arrival in Brazil.

After a tip-off, police raided the Costa Fascinosa cruise liner near the Canary Islands, off northwest Africa in March 2014. They found 25kg of cocaine heading towards Venice and Dubrovnik.

Investigators claim they were paid $10,000 for making the round trip but that the network employing them has made profits of tens of millions of pounds.

"This is new, a first," said Adid. "We are judging an international trade among three continents and the use of cruise ships."

He described the chief conspirators as "audacious innovators who had the ability to create new routes for cocaine".

Four of the accused – including Karim Moutakhaouil, the alleged ringleader – are on the run and being tried in absentia.

The trial continues.