French prosecutors said Thursday they had charged a subsidiary of US chemicals firm Lubrizol over a massive fire at a factory in northern France last September that coated the city of Rouen in acrid smoke.

Lubrizol France was charged with pollution and a failure to meet safety standards that resulted in "serious injury to health, security, or substantially degraded wildlife, flora, air, soil or water quality," the Paris prosecutor's office said in a statement.

Headquartered in Ohio, Lubrizol is owned by American billionaire Warren Buffett. The French-based factory produced lubricants and fuel additives.

Over 9,000 tonnes of chemicals burned in the September 27 fire outside Rouen, spewing smoke and soot over a 22-kilometre (14 miles) radius.

Locals complained about a thick deposit on everything, and many feared for their health.

More than 9,000 tonnes of chemicals burned on September 27, 2019 in a fire at the Lubrizol factory in Rouen, spewing smoke and soot over the area
More than 9,000 tonnes of chemicals burned on September 27, 2019 in a fire at the Lubrizol factory in Rouen, spewing smoke and soot over the area AFP / Philippe LOPEZ

Crops and animal products from the area were banned from sale for three weeks, affecting more than 1,800 farmers.

The blaze proved a flashpoint for public anger over environmental risks, especially after the lead contamination sparked by the April 15 fire at Notre-Dame cathedral in Paris.

Being charged under French law does not necessarily mean a person or organization will end up on trial.

Lubrizol France was also ordered to pay a holding amount of 375,000 euros ($411,650) and further security of four million euros, "to guarantee the rights of victims by allowing for the repair of human and environmental damage that may have been caused".

The amounts "correspond to the magnitude of the disaster," said the statement, while adding investigators have not yet established the cause of the fire.