China's coastal waters are suffering "acute" pollution, with the size of the worst affected areas soaring by more than 50 percent last year, an official body said.

The State Oceanic Administration (SOA) said 68,000 square kilometres (26,300 square miles) of sea had the worst official pollution rating in 2012, up 24,000 square kilometres on 2011.

Under this classification the waters are deemed unsuitable for swimming, fish-farming and port use and not fit for some industrial purposes.

The findings highlight the country's rising environmental problems, which are often a by-product of its booming economy and have led to public anger and protests.

"The pollution of coastal waters and damage to the eco-system... remained acute," the SOA said in a statement on the release of its annual report Wednesday.

Pollutants discharged into the sea from 72 monitored rivers increased to more than 17 million tonnes last year, the statement said, without providing a comparative previous figure.

That included 46,000 tonnes of heavy metals and 93,000 tonnes of oil, the state-run China Daily said Thursday, citing the report.

Plastic refuse accounted for 80 percent of litter in coastal waters, it added.

"Pollution discharge from land has sharply affected the sea environment," the SOA said in its statement, with high impact in major estuaries such as the Yangtze and Pearl river deltas which are huge industrial and population centres.

More than 80 percent of the Bohai Sea coastline in northern China was crowded with factories and construction projects, and less than five percent remained in a natural state, according to the China Daily.

China's Communist leaders have promised action on pollution in response to growing public outrage. Protests about environmental issues have reportedly grown by almost 30 percent a year since 1996.