BEIJING -- China's maritime authority on Sunday upgraded its wave warning from yellow to orange as Typhoon Wutip, the 21st of the season, approached land.

Boats return home seeking shelter as Typhoon Wutip approaches Wenchang, in China's southernmost province of Hainan. [Photo/Xinhua]

The central South China Sea is experiencing rough seas under Wutip's influence, according to the National Marine Environmental Forecasting Center.

From Sunday noon to Monday noon, waves as high as nine meters may occur in the western South China Sea, and waves of up to 4.4 meters may be spotted near eastern and southern coastal areas of South China's Hainan.

The center urged ships and coastal authorities to take precautionary measures.

It also warned of storm tides, with water levels expected to increase by as much as one meter from Sunday to Monday in Guangdong, Hainan and Guangxi.

Wutip is expected to make landfall on Vietnam's central coast on Oct 1, according to the center's report on Saturday.

China has a four-tier color-coded weather warning system, with red representing the most severe weather, followed by orange, yellow and blue.