"Today in Como is an important day. There are more than 10,000 of us taking part in this demonstration against all forms of fascism and intolerance," said Maurizo Martina, deputy secretary of Italy's centre-left Democratic Party (DP).
Among the crowd marching in the northern town of Como, a rally organised by an alliance of left-wing parties, was former prime minister Matteo Renzi.
Last week members of the far-right group Veneto Fronte Skinheads rushed an aid charity meeting in the town, denouncing "the migrant invasion".
Days later masked activists from another far-right organisation, New Force, stormed the Rome offices of the daily Repubblica and L'Espresso weekly brandishing smoke cannisters and calling for a boycott of the publications which they said supported immigration.
Earlier this week swastikas and other fascist insignia were daubed on the walls of a left-wing association in Udine, northeastern Italy.
More than 114,000 migrants have landed in Italy so far this year, down 32 percent on the same period in 2016.
Some observers have blamed the resurgence of fascism on rivalry between right-wing groups in the country.