Italian news media reported Friday that an Italian man — a partner in the company that owned the building — was also under investigation.

There are nearly 16,000 legal Chinese residents in Prato, a city of 191,000. Estimates for the number of Chinese people living here illegally fluctuate from 15,000 to 25,000, and the exact figure is “unknowable,” officials say.

Law enforcement and health officials have carried out 1,571 checks on businesses in Prato over the last two years, Labor Minister Enrico Giovannini told the Italian Parliament on Tuesday. More than half of those businesses belonged to Chinese citizens. The checks were part of Italy’s effort to “confront conditions of unsustainable illegality and exploitation,” he said.

More than 1,700 fines have been issued to companies for not paying social security contributions, while about 400 people living in the country illegally have been identified, Mr. Giovannini said. More than 350 companies were closed and production was halted for various violations.

In many cases, said Aldo Milone, the municipal council member responsible for the city’s security, “the situation inside the businesses we checked had the same characteristics as in Teresa Moda.” After the fire, several wholesale stores adjacent to the burned factory were shut down after firefighters found dormitories inside.

But the problems always seem to stay one step ahead of discovery. Officials say many businesses here open and close before health or fire inspectors, and even the tax police, can check them. Often they reopen with new tax code numbers.

And while in Prato there is sympathy for the victims and outrage at the Dickensian conditions under which they lived and worked, the fire in the outlet-turned-factory also exemplified what some Italians say angers them most. Chinese businesses, they say, have flourished while Italian companies have failed because the Chinese ones depend on poorly paid labor and have ignored workplace safety standards in the name of cutting costs.