Prosecutors in eastern China have filed a lawsuit against a county-level environmental protection department, accusing it of "failing to fulfil its regulatory duties" in its supervision of a local sewage firm, China's top prosecutor said.

China's Supreme People's Procuratorate said the lawsuit filed by prosecutors in eastern Shandong province last week marked the first time prosecutors had sued a government department in a public interest case.

"This is the country's first administrative public interest litigation case after the National People's Congress authorized prosecutors to file public interest lawsuits in a pilot program," according to a statement from the Supreme People's Procuratorate on its website.

The National People's Congress is China's largely rubberstamp parliament body.

The suit comes after China's leadership has vowed to crack down on severe levels of air, water and soil pollution, including the heavy smog that often blankets major cities, following decades of unbridled economic growth.

The work of environmental departments has come under extra scrutiny because of public discontent over the environment. Experts say that local governments have pressured courts not to go hard on polluting industries that drive their economies.

Prosecutors in Qingyun county in Shandong had investigated a local sewage firm over allegations that it lacked environmental protection facilities, according to China's top prosecutor. The department imposed only nominal administrative punishments and committed "illegal acts", it said.

In January, China's Supreme Court said it would give environmental groups the power to sue before any pollution had occurred if they could show that a particular activity could threaten the public interest.