About 20 members of Extinction Rebellion and Marseille-based Stop Croisieres (Stop Cruises) made a chain of canoes in the water across the entry to the port, an AFP correspondent reported.

The demonstration forced one ship to turn back at 7:00 am (0500 GMT) and moor further down the coast. Others had to stay in stand-by outside the port until about 9:30 am.

The activists were removed and the port has since reopened, the maritime authorities told AFP.

"Nothing justifies the maintenance of these absurd, energy-intensive and toxic floating cities," Stop Croisieres said on its website.

"Our air, our seas and our health are not up for negotiation," it said.

It criticised the noxious heavy fuel oil used by the vessels, the destruction of ocean and coastal wildlife, the ships' impact on the climate and poor working conditions for employees on board.

The protest prevented the Germany-owned Aidastella, which can carry around 2,000 people, from docking at around 7:00 am.

The Costa Smeralda and the MSC World Europa also had to wait before entering the port.

The MSC World Europa is the sixth largest cruise liner in the world. It can carry 6,000 passengers and has more than 2,600 cabins, as well as 13 restaurants and a shopping centre.

The Cruise Lines International Association condemned the protest as "illegal and dangerous".

In an email to AFP, it argued the cruise liner industry was pursuing efforts to cut emissions of climate-heating greenhouse gases.

- Pollution -

Marseille is the centre of a burgeoning cruise ship industry in France.

Between 2022 and 2023, the number of cruise passengers entering the port jumped from 1.5 million to 2.5 million, according to the Marseille tourism observatory.

Advocates of cruise liners argue they provide revenue to stopover ports.

Detractors say the ships encourage passengers to spend their money onboard, not on land, and that the industry promotes competition between reception ports to force down prices.

There have been protests in several European port cities against the damage caused by cruise liners, including in Venice and Amsterdam, which have banished them from docking in the city centre.

Stop Croisieres was set up during the Covid pandemic.

"We saw videos of nature being restored all over France, little birds in towns and other bucolic scenes," said Andrea, who declined to give her surname for fear of prosecution.

"Yet in some parts of Marseille, the air was even more polluted than before the pandemic because of all the cruise liners forced to stay in port with their engines running."

In March 2023, residents' associations in Marseille lodged a legal complaint over ocean traffic pollution in the port area, which regularly exceeded European Union limits.

According to a study by NGO Transport and Environment, cruise ships sailing in European waters in 2022 emitted more than eight million tonnes of carbon dioxide -- the equivalent of 50,000 Paris to New York flights.