Some 30 vessels with crude and oil products were blocked at Fos-Lavera near the Mediterranean port of Marseille, one of the world's biggest ports, up from 27 on Monday.

On Corsica, fully dependent on supplies from Marseille, only emergency vehicles had access to petrol stations as the French island was expecting a boat with gasoline on Wednesday to help it ease the fuel crisis, the local authorities said.

A source at the CGT union, which has led the movement, said late on Tuesday that strikers had decided to prolong their action until Wednesday, when they are due to meet other unions in a bid to join forces in a move that could drastically cut gasoline supplies to pump stations.

"The port has offered all possible job guarantees to the strikers, what else can the port offer?" a port spokeswoman said.

The strikers want job guarantees as part of a port reform and are also protesting against President Nicolas Sarkozy's pension reform to raise the retirement age to 62 from 60, which has already sparked several waves of nationwide protests.

France's next big day of national strikes is set for Oct. 12, coinciding with the date cited by unions for some refineries to halt production due to crude oil shortages.

The CGT union is trying to use the Fos-Lavera blockade as a lever for a national cross-sector strike to defeat the government on the controversial and unpopular pension reforms.

On Tuesday, ICE gas oil futures eased down from a five-month high ahead of an expected influx of distillates from Asia and the United States.

A fleet of cargoes carrying 400,000 tons of the motor fuel diesel was set to arrive in northwest Europe in the first half of October from the US Gulf, traders told Reuters.

France's oil industry lobby and a Transport Ministry source said three-month strategic oil stocks were so far untouched despite union officials saying Total's La Mede refinery had started using them.