The National Marine Environmental Forecasting Center upgraded the rainstorm alert for Typhoon Nalgae to the orange level on Monday afternoon.
Orange is the second-highest alert level in the country's four-level rainstorm alert system.
The center warned that a number of tidal stations off Hainan, Guangdong and Fujian provinces will see tides exceeding safety levels.
Nalgae was located over the South China Sea, 350 kilometers from Sanya City of the southmost Hainan Province at 4 p.m. Monday.
Waves of 2 to 5 meters high have been observed in the waters off Guangdong, Hainan, Fujian, and Zhejiang provinces according to a statement issued by the forecasting center on Monday afternoon.
Waters off east Hainan province will see waves of 3.5 to 5 meters high from Monday night to Tuesday, the East China Sea and Taiwan Strait will see waves of 3 to 5 meters high, and waters off Fujian, Guangdong and Guangxi will also see waves of 2 to 4 meters high, according to latest forecast.
The center warned tourists heading to typhoon-hit provinces to be flexible with their itineraries as several air and ship routes might be affected.