Italian prosecutors have asked for some 300 Chinese nationals and the Bank of China's Milan branch to be tried for money laundering and tax evasion.

Prosecutors in Tuscany made the request following a probe into criminal networks in the region, long home to a large Chinese community that has drawn fire in the past for running clothes factories in sweatshop conditions.

The investigation, dubbed "River of Money", began in 2008 and focused on money transferred to China -- funds Florence prosecutors say come from exploiting illegal labour, counterfeiting money and tax evasion, according to Italian media reports.

Those under investigation are accused of using the Money2Money (M2M) transfer service to shift money from several Italian cities, with the Bank of China receiving over 750,000 euros ($850,000) in commissions, the reports say.

The daily La Repubblica said that between 2006 and 2010 over 4.5 billion euros ($5.1 billion) was smuggled to China, with 2.2 billion euros going via the Bank of China's (BOC) Milan branch.

Denouncing it as an "awe-inspiring hemorrhage of money to China while Italian businesses were dying, torn apart by Chinese competition", the daily said 287 Chinese citizens in Italy were being probed, along with four bank officials.

The case will now go before a judge for a decision on whether to press charges.

The Tuscan town of Prato -- dubbed Italy's Chinatown -- hit the headlines in 2013 when a deadly fire in a garment factory left seven people dead.

Chinese immigrants began arriving in Prato some 20 years ago, initially working for Italian companies before setting up their own businesses.

There are now around 17,000 Chinese in a population of 188,000 -- 50,000 if the estimated number of undocumented immigrants are included.

The money being sent abroad was divided up into sums smaller than 2,000 euros in a bid to avoid detection, the reports said.