French maritime officials said the ship was carrying 1,700 tonnes of dangerous materials, including battery acid, explosive and flammable material.
The containers also hold motorcycles, car parts and oak barrels.
Britain's transport department said more than 200 containers from the ship, which was listing at a 30-degree angle, slipped into the sea as new gales struck the English coast late Saturday.
Paul Coley, a maritime and coast guard spokesman, said two of the containers that went overboard contained hazardous materials including battery acid and perfume products. He said the risk they posed was "minimal".
He said: "About 200 tonnes of oil has been lost. We still believe that no major tanks have been breached."
Threat from diesel
Robin Middleton, the government's salvage adviser, said a greater threat was posed by the ship's 3,000 tonnes of diesel and fuel oil, some of which had leaked out through a crack in the vessel's port side.
Middleton said only one fuel tank appeared to be ruptured, with no more than 200 tonnes of oil likely to leak.
He said salvage workers would attempt to stabilise the ship to prevent it capsizing, pump out the fuel oil and remove the containers.
The 16-year-old vessel is registered in London and was last inspected by the coast guard agency in May 2005, when officials said it met safety standards.