The cold front responsible for the current cold snap is set to be the strongest so far this year, and yesterday the Shanghai Meteorological Bureau issued a blue cold wave alert, the lowest of a four-level system.

The bureau warned that the mercury could drop by 8 to 10 degrees Celsius within 48 hours, with the wind reaching 50 kilometers per hour.

Forecasters warned locals, especially those who work indoors, not to be fooled by the mild temperatures yesterday morning. 

Officials said the mercury reached a high of 14 degrees in the morning. By 2pm it plunged to 10.4 degrees, 8.4 degrees lower than the same time on Sunday.