A fire at a French chemical factory which deposited a blanket of oily soot on plants for miles around, had cost farmers an estimated 40 to 50 million euros ($44-55 million), the agriculture minister said Friday.

The government banned the harvesting of crops or the sale of animal products from a wide swathe of tainted countryside around the town of Rouen in northwest France in case the chemicals burnt at the Lubrizol factory last month had given off toxins.

The Lubrizol plant, owned by US billionaire investor Warren Buffett, makes industrial lubricants and fuel additives just a few kilometres (miles) from the centre of Rouen, a city of some 100,000 people where anger is rife about the government's perceived failure to communicate the full risks of the smoke and soot.

The cause of the blaze, which left the region with a foul smell for days on end, is not yet known. Minister Didier Guillaume on Friday spoke of an "economic drama", with milk producers alone losing about four million euros' worth of milk.

"All sectors must be compensated as soon as possible," the minister told journalists on a visit to Rouen.

The newspaper Les Echoes reported Friday that Lubrizol had agreed to set up a fund of about 50 million euros to cover the losses of farmers and other industries affected by one of France's worst industrial fires in recent times.

It would also directly compensate about 450 farmers in the region hit by a ban on milk production in the wake of the blaze which consumed over 5,000 tonnes of chemical products and spewed a smoke cloud some 22 kilometres (14 miles) wide.

Copyright Agence France-Presse, 2019