Three Chinese and Taiwanese staff members of an Australian currency brokerage who were held against their will by angry investors in Shanghai have now been freed by police.

The trio and their colleagues were working for Sydney-based Union Standard Group Forex (USGFX) when around 50 people stormed the office last Wednesday.

Most of the employees were allowed to leave, but the intruders kept three in the office, allegedly threatening them with violence.

A USGFX representative says the staff were provided with food and water only after they pleaded for it, and at least one person suffered minor injuries.

USGFX says it has employed lawyers to handle the case. ( Supplied: USGFX )

Despite police saying they were handling the case, the three employees were forced to remain at the office over the weekend and into Monday.

It is understood a large number of police arrived at the building in Xuhui district on Monday to safely escort the staff to a police station.

The ABC spoke to one of the investors involved in occupying the office, who did not want to give her name.

"I became their client, within three days, I lost all my money", she said.

USGFX says one third-party broker using the firm's currency trading platforms lost $AUD 3.28 million of investors' money on July 18 while trading between the Australian and US currencies.

China's financial sector has come under increasing scrutiny in recent months. ( Supplied: USGFX )

Staff are now helping police with what is understood to be an investigation into USGFX's trading practices.

A USGFX representative says the remaining staff members are not currently able to return to work at the office.

The firm says it has also employed lawyers to handle the case.

China's financial sector has come under increasing scrutiny in recent months, as the government seeks to clamp down on risky wealth management products that have attracted investors seeking better returns than what state-owned banks can offer.