BEIJING - China's top meteorological authority on Thursday issued a blue alert as Typhoon Krosa is set to arrive in the South China Sea before dawn on Friday.

Krosa, the 29th typhoon to hit China this year, strengthened to a strong typhoon on Thursday afternoon. It is forecast to move with a speed of 20 km per hour toward south China's Guangdong and Hainan provinces, the National Meteorological Center (NMC) forecasted.

The typhoon is packing winds with a force of up to 42 meters per second, according to the NMC.

Krosa will bring strong winds and torrential rain to Taiwan, Fujian, Guangdong as well as the Taiwan Strait, the center said.

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