China's top observatory on Sunday evening issued a yellow alert for tropical storm as Typhoon Kalmaegi was approaching the South China Sea.

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

Typhoon Kalmaegi is forecast to reach the eastern waters of the South China Sea on Monday morning when the scale is expected to weaken to 35-40 meters per second, said the National Meteorological Center (NMC).

The storm will then move westward to Guangdong Province and the eastern part of Hainan Province when its intensity is expected be strengthened to 45-50 meters per second.

Kalmaegi will affect the southern and southeastern coast from Sunday evening to Monday evening, said the NMC.

The observatory also forecast parts of the east region of northwest China, Sichuan Province, Chongqing Municipality, and north China to experience medium-to-heavy rain.