The number of illegal immigrants entering Italy doubled in the first seven months of the year compared to the same period in 2007, Rome says.
The figures come in spite of a government crackdown on crime and an increase in the number of deportations.
More than 15,000 illegal immigrants entered the EU via Italy between January and July, Interior Minister Roberto Maroni said.
Many illegal immigrants arrive on boats organised by people traffickers.
Mr Maroni, whose Northern League party formed part of the right-wing government coalition, has campaigned strongly against clandestine immigration.
Most of the illegal immigrants come across the Mediterranean Sea from North Africa.
Italian Prime Minister Silvio Berlusconi has launched a crackdown on crime, which most Italians associate with illegal immigration.
He brought in stringent new measures making it an offence punishable by up to four years jail to enter the country illegally.Prisons full
Expulsions have increased by 15% so far this year but the Italian authorities often find the countries of origin of illegal arrivals reluctant to accept them back if they are deported.
Two weeks ago the authorities began deploying troops in joint anti-crime patrols with police in some of Italy's major cities.
Thirty-three non-EU nationals have been arrested so far. Italy's prisons are already crammed with foreigners.
Some 20,000 people out of the 55,000 prisoners currently serving sentences or awaiting trial in Italian jails are foreigners.
The number of these foreign prisoners continues to increase because of the expense and difficulty of executing expulsions ordered by the judiciary.
Many Italians associate illegal immigration with crime