Son-Tinh, the 23rd tropical storm this year, strengthened to typhoon early Saturday morning and is expected to bring rainstorms and gales to China's southern coastal areas, the country's meteorological authority said Saturday.

The National Meteorological Center of China said the center of Son-Tinh, which is gaining strength, was 75 kilometers to the southwest of Sansha, a newly established city in the South China Sea, at 5 a.m. Saturday. It was moving northwestward at a speed of 20 to 25 km per hour.

The approaching Son-Tinh is expected to bring heavy rainfall and strong wind to the southern parts of China, including parts of Hainan Province and Guangxi Zhuang Autonomous Region in the coming two days.

Sansha and southern parts of Hainan will be hit the hardest by downpours, according to the meteorological center.