Sixty percent of underground water in China which is officially monitored is too polluted to drink directly, state media have reported, underlining the country's grave environmental problems.

Water quality measured in 203 cities across the country last year rated "very poor" or "relatively poor" in an annual survey released by the Ministry of Land and Resources, the official Xinhua news agency said late Tuesday.

Water rated "relatively" poor quality cannot be used for drinking without prior treatment, while water of "very" poor quality cannot be used as a source of drinking water, the report said.

The proportion of water not suitable for direct drinking rose from 57.4 percent from 2012, it said.

China's decades-long economic boom has brought rising environmental problems, with large parts of the country repeatedly blanketed in thick smog and both waterways and land polluted.

Pollution has emerged as a driver of discontent with the government, sparking occasional protests.

China's environment ministry last week estimated that 16 percent of the country's land area was polluted, with nearly one fifth of farmland tainted by inorganic elements such as cadmium.

Premier Li Keqiang announced in March that Beijing was "declaring war" on pollution as he sought to address public concerns, but experts warn that vested interests will make it difficult to take action.

Many Chinese city-dwellers already avoid drinking tap water directly, either boiling it or buying bottled supplies.

Residents of the western city of Lanzhou rushed to buy mineral water earlier this month after local tap water was found to contain excessive levels of the toxic chemical benzene, state media reported at the time.

A subsidiary of the country's largest oil company, China National Petroleum Company, was blamed for the incident after oil from one if its pipelines leaked into the water supply.

The Lanzhou government also came under fire for reportedly failing to notify locals of the pollution for several days after becoming aware of it.