A rare mantle of snow blanketed the historic centre of Rome Friday, forcing the closure of schools and tourist sites such as the Colosseum as Pope Benedict XVI took a peek at the snowflakes.

The snow covered palm trees, ancient Roman ruins and Baroque churches across the normally mild-weather Italian capital which has only seen one snowfall in the past 15 years in which the snow stayed on the ground for a whole day.

"Avoid moving around unless strictly necessary," Rome mayor Gianni Alemanno advised residents of the Eternal City on TG1 news channel, as the civil protection agency ordered all emergency services to be on high alert.

Schools and municipal offices have also been closed down and teams of 400 volunteers were driving around the city to help dig snow away from schools, pharmacies and hospitals, as well as aiding cars trapped in the snow.

Like the Colosseum, the Via dei Fori Imperiali was closed off to tourists and some cars could be seen driving around the city in snow chains.

In the Vatican, a smiling Benedict was spotted peering out of his window at the snowflakes.

Temperatures in the Alpine region of Piedmont in northern Italy meanwhile went as low as minus 30 degrees Celsius (minus 22 Fahrenheit).

The weather caused flights delays in northern Italy and traffic was backed up on several motorways in central parts of the country. The interior ministry advised drivers to avoid large parts of central Italy if possible.

A bus with 45 elderly passengers was stuck in snow for three hours in a mountain town near Naples and had to be evacuated by emergency workers.

A train from Ancona to Roma was also blocked for four hours by the snow near Perugia and eventually had to return to its point of departure.

Three people have died due to the extreme weather in recent days, with the latest victim a homeless man found in the centre of Milan on Thursday.

Snow and freezing temperatures are forecast to continue into Saturday.