The facility in the city of Gabes emits sulphur gases, nitrogen and fluorine, according to an audit last July for the African Development Bank, which reported "major non-compliance" on air and marine pollution.

Mounir Adouni, head of the Gabes bar association that launched the legal action, said Thursday's decision was an emergency ruling and a final verdict was pending.

"The court ruled that there was no sufficient proof of harm, saying allegations of pollution lacked technical and scientific evidence," Adouni said.

A major Tunisian civil rights group condemned the ruling, calling it a "serious setback in the treatment of the country's biggest environmental pollution case".

"The argument that there is no evidence of harm can only be seen as a blatant disregard of established and documented facts," the Tunisian Forum for Social and Economic Rights added.

It said the pollution was not an allegation but "confirmed by official reports".

Locals in Gabes have for years rallied against the phosphate-processing factory, which makes fertilisers mainly for export.

The bar association lodged its complaint after thousands protested against the plant in October, blaming it for an increase in health problems in the local community.

This month local campaign group Stop Pollution said 12 of its members had been sentenced to a year in prison over a 2020 protest at the plant.

Adouni said the bar will file an appeal on Friday because no date had been set for a hearing on a final ruling.

Despite a 2017 promise to gradually shut the plant down, authorities last year said they were ramping up production.

Taking advantage of rising prices for fertiliser on global markets, Tunisia now wants its output to increase more than fourfold by 2030.

The African Development Bank last month said it would provide Tunisia with $110 million to "support the environmental upgrading and rehabilitation" of the factory.

President Kais Saied has long vowed to revive Tunisia's phosphate sector, hindered by years of underinvestment and unrest, calling it a "pillar of the national economy".