French authorities have seized a large haul of methamphetamine with an estimated street value of nearly six million euros, prosecutors said on Friday, adding that two people had been charged over the find.

The drugs seized in southeastern France on June 18 weighed 216 kilogrammes (476 pounds), Marseille chief prosecutor Nicolas Bessone told reporters, having called the haul "exceptional" in an earlier statement.

By comparison, the total amount of methamphetamine seized nationwide in 2022 stood at 273 kilogrammes, according to data from the interior ministry for the most recent year available.

Investigators latched onto the trail of meth producers when customs inspectors found 5.6 tonnes of chemical precursors in the port of Le Havre in northern France in September, Bessone said.

Precursors are legal products that can be used by pharmaceutical or perfume manufacturers but also to produce illegal drugs.

Following up on their probe, police arrested two people "loading substances into a vehicle from a storage unit located in the centre of the Var department, near Brignoles," a town between Marseille and Saint-Tropez, Bessone said.

They found 21 cardboard boxes containing methamphetamine, as well as more than 500 rounds of 7.62-millimetre ammunition and a 9-millimetre pistol with ammunition.

Kalashnikov rifles firing 7.62-millimetre rounds have been used in the growing number of gangland killings in Marseille linked to the drug trade.

The two suspects aged 47 and 40 had previous convictions for selling drugs, and have now been charged over drug production and carrying banned weapons.

They are being held in provisional custody.

"France has traditionally been a country precursors transit through on the way to places like Belgium and the Netherlands, but there's a new trend developing that we believe includes production in France," a representative of the DNRED customs investigation agency told AFP.

According to a police source, the average retail price of highly addictive methamphetamine stood at 27 euros (nearly $29) per gramme in 2023.

The United Nations Office on Drugs and Crime has warned that methamphetamine, the world's most widely used synthetic stimulant drug, is one of the greatest threats to global health.

Usually ingested as a white powder or a pill, the drug is known under various street names including "yaba" and "ice".

In June 2019, nearly 400 kilogrammes of methamphetamine were seized by authorities from a truck travelling in eastern France.

Less than a year later, in February 2020, customs officials intercepted a truck carrying 175 kilogrammes of the drug in the southwestern department of Pyrenees-Atlantiques, close to the Spanish border.