China's sea level hit a record high in 2012 due to global warming and land subsidence, threatening millions of coastal residents, according to a government report.

The State Oceanic Administration report released on Tuesday said that last year, the sea level rose 122 millimeters more than the average level from 1975 to 1993, about 53 mm higher than 2011.

"The rising temperatures from increasing greenhouse gas emissions and the land subsidence nationwide led to the high seas," said Liu Kexiu of the National Marine Data and Information Service.

Average air temperatures in coastal areas rose 0.4 C above the average from 1975 to 1993 in 2012, and sea temperatures rose 0.3 C, according to the report.

High seas can aggravate storm tides, exacerbate monsoon flooding, erode shorelines, cause seawater invasion and inundate crops, homes and livelihoods at great risk.

Scientists estimate the situation will be worse in 2050, when sea levels may rise up to 200 mm and submerge about 87,000 square kilometers of coast, the report warns.

By 2100, about 20 percent of the sand area in the Dadonghai beach in Sanya, Hainan, is predicted to be under water.

Sea levels rise when oceans absorb large amounts of heat and the global warming accelerates melting from land-based ice such as glaciers.

In 2012, China was hit by 24 storm tides, causing economic losses of nearly 13 billion yuan ($2 billion), about 32 percent more than the average damage caused during the past five years, the report said.

Storm tides damaged 897 ships and ruined nearly 116 km of shoreline in Zhejiang province, causing more than 4 billion yuan in direct economic losses.

Wang Feng, director of the SOA's marine forecast and disaster relief department, said the Liaoning, Jiangsu and Shandong province coastlines were harder hit by the rising sea than the rest of the country in 2012.

The report said due to the higher sea level, the shoreline in Suizhong, in Liaoning, has retreated about 60 meters since 2000, and about 18 km from the coastline in Panjin was covered by seawater, leading to soil salinization.

The effects of land subsidence in 2011 pushed the ground in Tianjin Binhai New Area at least 3.4 meters lower than in 1959, according to data, which will worsen the effects of the rising sea level.

Besides the increasing marine disasters, land losses and shoreline damage caused by the sea level rise, Wang also worried about the inundation of base point islands in the South China Sea. The SOA is accelerating the protection and monitoring of base point islands.

To control the sea level rise, the SOA is classifying coastal areas according to the risk from climate change and rising sea levels, providing guidance in marine economic development and large-scale projects, Wang said.