As a row erupted over the efficacy of the measures, Milan and the nearby town of Pavia banned cars from their roads between 10 am and 4 pm for three days starting Monday.

In Rome, owners of cars with odd-numbered plates were ordered to leave them at home for the day. On Tuesday, cars with even-numbered plates were targeted under a measure used three times this month with limited effect.

Traffic restrictions were also in place in the southern city of Naples, where only vehicles operating to an emissions standard known as Euro 4 are allowed to circulate this week.

With many Italians on holiday between Christmas and New Year, the measures were seen as largely symbolic and the authorities have been attacked for backing them up with only limited enforcement measures.

Air pollution contributed to 84,400 premature deaths in Italy in 2012, according to the latest report for the European Environment Agency. Of these 59,500 were attributed to elevated levels of fine dust particles in the air, the problem which has caused this week's alerts.

"This morning, the streets were deserted but it's not only because of the driving ban. Am I the only person working this Monday?" one Milan resident wrote on Twitter.

After several weeks with little or no rain in much of Italy and weather balmy enough to have sent many Romans to the beach for their Christmas lunches, pollution levels measured by the number of fine dust particles in the air have shot up.

Numerous locations have exceeded the 50 mg per cubic metre level which the World Health Organization regards as a ceiling which should not be exceeded in the interests of the general wellbeing of urban populations.

The traffic ban "is a response to an exceptional emergency," the city's mayor Giuliano Pisapia said. "The measure does not bring the city to a standstill but it does have a strong deterrent effect."AFP