Italian police on Wednesday launched a crackdown on illegal immigration from China, just hours before President Xi Jinping arrived on a flying visit that Rome hopes will bolster ties.

In an operation code-named "White Collars", the GDF financial police said they had ordered 15 arrests and 111 raids on premises across five regions and placed another 83 people under formal investigation.

The moves were ordered by a prosecutor based in Prato near Florence, home to one of Europe's largest Chinese communities.

Some 400 officers were deployed as part of an investigation into a racket involving the forging of payslips and other documents to help secure residency permits, the GDF said in a statement.

It added that the investigation was focused on a number of Italian and Chinese professionals and businessmen, most of them based in Prato.

Xi touched down on Wednesday on the Italian island of Sardinia for an overnight stop en route for a three-country tour of Latin America.

The Chinese President was due to visit the ruins of the ancient town of Nora, one of the island's most important archaeological sites, before being entertained by a Sardinian folk band.

- Strained relations -

Xi was to be entertained at dinner by Matteo Renzi, the Italian prime minister who has made boosting trade and investment links with Beijing a priority for his centre-left administration.

Relations between the police and the Chinese community in Prato were strained earlier this year when a raid on a textile factory suspected of breaching labour laws ended in violent clashes involving 300 people, two arrests and injuries to four policemen.

Beijing made representations to the Italian authorities over the June incident, urging them to ensure that Chinese nationals were not being targeted unduly.

Days after the mini-riot, police made a series of raids connected with an investigation into a Chinese association suspected of organising vigilante patrols of Prato's Chinatown which allegedly targeted African and Arab residents.

- 'Rules are rules' -

Italy is home to more than 270,000 Chinese nationals. A fifth of them are self-employed and the Leone Moressa foundation estimates that the community contributes six billion euros ($6.42 billion) a year to the Italian economy.

But the Chinese are also regularly accused of not adapting to Italian life, of sending millions in untaxed profits back to China and of sidestepping labour and immigration laws.

Officials in Prato say sweatshop exploitation in the textile sector has diminished since a 2013 fire in a garment factory left seven people dead.

It emerged afterwards that the workers had been living in the factory and were unable to escape as the windows were barred.

Local officials welcomed Wednesday's police action.

"It has to be done," Prato's mayor, Matteo Biffoni, told AFP on the sidelines of a conference in Rome.

"Those who respect the rules are welcome. Those who bend them hurt the interests of Italians and other immigrants. There has to be zero tolerance on this point. An investigation is underway and we will see what happens, but rules are rules and there has to be a price for not respecting them."

Prato is officially home to some 16,000 Chinese nationals out of a total population of 191,000. But local sources say the real figure could be closer to 50,000.

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