BEIJING -- China's national observatory on Sunday issued a blue alert for a cold wave as freezing air is expected to sweep across vast parts of the country in the coming days.

From Nov 16 to 18, the cold wave will bring strong winds and sharp temperature drops to central and eastern regions, with daily averages or lows falling by 6 to 10 degrees Celsius, according to the National Meteorological Center.

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Notably, temperatures in parts of Shaanxi, Chongqing, Henan and Hubei could drop by 12 to 14 degrees Celsius, the center said.

It urged relevant departments to step up preparations and called for precautionary measures to protect tropical crops and aquaculture from the cold.

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