SHANGHAI (REUTERS) - China has promised to take action to "significantly reduce" the volume of industrial waste water flowing into the Bohai Sea, one of the world's busiest and most polluted shipping routes, the Environment Ministry said on Tuesday (Dec 11).

China has been struggling to reverse the environmental damage done to the Bohai Sea, which stretches along the coast of the major heavy industrial provinces of Liaoning, Hebei and Shandong. Its waters have been contaminated by sewage, heavy metals, plastic waste and fertiliser run-off.

Served by major coal, iron ore and crude oil ports like Dalian, Tianjin, Caofeidian and Qinhuangdao, the Bohai Sea was also the location of a 2011 oil spill from a well operated by the US firm ConocoPhillips.

The Ministry of Ecology and Environment said in a new policy document that it would take action to ensure that around 73 per cent of Bohai coastal waters are fit for human contact by 2020.

It did not say how much was fit for human contact now.

The document also said the ministry would establish and enforce ecological "red lines" that would put parts of the coast off limits to development, and restrict land reclamation and shoreline development.

China aims to set up a regular inspection team to ensure laws are being enforced and help prevent marine oil spills and other environmental risks, according to the document.

Mr Ke Chang, the head of the ministry's marine environment office, told reporters at the end of November that China has been unable so far to resolve major coastal pollution problems in Bohai or reduce the flow of pollutants entering the sea.

China aims to put around 30 per cent of its coastal waters off limits to development as part of its ecological "red line"scheme, Mr Ke said.