Foggy weather affecting a large part of the country has caused traffic jams on expressways on Friday, as a seven-day toll-free policy brings more cars to the roads.

Data from the Ministry of Transport showed traffic on 10 major monitored expressways surged 40 percent on Friday compared to the previous day, as the policy to exempt tolls for passenger vehicles began on the same day.

A total of 75 expressways stretching across 13 provinces were jammed since Thursday, while many expressway sections in Hebei Province remain closed as of 3 p.m. due to heavy fog, the data showed.

China's national meteorological authority also issued an alert as heavy fog will continue to shroud central and eastern China on Friday.

Friday is first day of a seven-day break for the Chinese to celebrate the on-going Spring Festival.