Japanese police are investigating a possible human trafficking ring after arresting 11 Chinese construction workers over visa violations and finding that 46 other labourers appear to have fled.

About 60 Chinese labourers arrived in September and were dispatched to the island of Hokkaido from a company near Tokyo to build a giant solar power plant, according to Japanese reports.

Some of those detained by Japanese authorities have said they were “deceived” by an intermediary about the work involved in Japan.

Authorities were alerted to the case when a Chinese man died on Nov 26 after he was taken to a local clinic by four other workers, according to a statement posted Tuesday by the Chinese consulate in Sapporo.

Those four men have since gone missing.

On the same day as the death, police arrested 11 Chinese people aged 27 to 62, finding two were without passports with the remaining nine allegedly having overstayed their visas.

The Chinese workers reportedly lived in housing roughly 11 miles away, and entered Japan through the port of Nagasaki or by plane in Tokyo, and were brought to the plant by a staffing agency.

Japanese authorities are looking specifically into whether the employer knew the Chinese workers lacked proper documentation.