Dutch-based Smit Salvage, contracted to remove oil from the partially submerged ship, said on Friday one of its tugs hit the partially submerged wreck and cracked the Tricolor's hull in bad weather on Wednesday.

"Due to the high swell she was picked up by a wave and hit the wreck in a very unfortunate place -- directly on a tank holding oil," Smit's Lars Walder told Reuters.

Walder said the tank held some 170 tons of ship fuel but added it was not clear how much had seeped out.

He said the crack was quickly patched up and the oil leak contained early on Thursday morning.

"We hear from the French authorities that there is an oil leak that is approximately seven kilometers to eight kilometers long but it is very thinly dispersed on the surface."

A spill response vessel with an oil boom was heading to the scene to suck up the oil.

The Tricolor sank with a cargo of luxury cars worth up to $50 million after smashing into a container ship in the busy shipping lane in mid-December.

A few days later, a German cargo vessel crashed into its hull, which lies in French waters about 25 meters (82 feet) deep and is visible only at low tide.

In early January the wreck was struck again, this time by an oil tanker, the Vicky, carrying 70,000 tons of highly flammable kerosene.