BEIJING - Typhoon Son-Tinh is expected to cause high waves in the South China Sea with the country issuing an orange level wave warning on Saturday morning.

The National Marine Environmental Forecasting Center said the tropical storm developed into a typhoon early Saturday morning and was heading toward the northwest with the same strength or slightly gaining force.

Orange alert is the second highest level on China's four-tier color-coded warning system for strong winds.

Son-Tinh is expected to sweep the South China Sea off Hainan province during Saturday night. As the Typhoon approached, waves of five to eight meters had been seen in the east of the South China Sea.

According to the forecast, waves up to five to eight meters will be seen in the west part of the sea in the 24 hours starting Saturday noon.Waves of three to five meters will be seen in the Northern Bay.

Waves up to 3.5 to 4.5 meters high will hit seas off the eastern and southern Hainan province. There could also be waves of two to three meters off the western Hainan province and Guangxi Zhuang autonomous region.

The center warned ships and people in affected areas to be careful urging authorities to take full precautions.

It has forecast up to 80 cm of precipitation on Saturday along the coast of eastern and southern Hainan province and eastern coast of Leizhou peninsula.

The center called on local authorities to expect high tides by reinforcing fishing facilities and sea walls in susceptible areas.

It also issued a blue alert for storm surges. China's four-tier warning system consists of red being the most serious, followed by orange, yellow and blue.