Milan's mayor imposed a two-day ban on traffic in the city and closed schools on Friday in a radical move to battle smog in Italy's industrial heartland, despite fierce protests from shopkeepers.

Giuliano Pisapia banned traffic from circulating between 0900 GMT and 1700 GMT on Friday and Saturday. While blocks on traffic in the business capital are not uncommon, they are usually restricted to weekends.

Pisapia also closed schools on Friday, though many children may have been absent anyway as their families extended Thursday's bank holiday into a long weekend.

The mayor's office said 43 police patrols were deployed throughout the city to enforce the ban and issue fines of 155 euro (207 dollars) to rule-breakers.

Highly polluting vehicles manufactured before 2001 are banned from the city's roads until December 23.

Pisapia's decision was criticised by shopkeepers who argued that it would affect pre-Christmas sales.

"The seriousness of the pollution means we cannot wait to act," Pisapia said, adding that shops would be given special permission to stay open until midnight on Saturday.