A former banking magnate and 50 others went on trial in Vietnam Monday over a multi-million dollar fraud at a major private bank, as the nation cracks down on corruption in the sector.

Authorities have vowed to clean up an industry plagued by favouritism and dodgy loans -- part of a broader drive against corruption in the country.

In the latest trial, the ex-chairman of Ocean Bank, Ha Van Tham, is accused of illegally approvingloans worth US$23 million in 2012, ultimately leading to the bank's demise and stripping him of his status as one of the country's richest men.

Tham and 50 other bankers and businessmen, most of whom worked at Ocean Bank, face various charges related to the illegal loan in the 20-day trial that opened Monday.

Some face the death penalty, according to the lengthy indictment.

The trial involves a record 50 defence lawyers and more than 700 witnesses, and is the second time the accused have appeared after a March trial was postponed for further investigation.

Tham is accused of approving the loan to the Trung Dung real estate company without proper collateral.

The head of the real estate company, Pham Cong Danh, is currently in jail for a separate conviction of economic mismanagement.

Ocean Group, which includes real estate and hotel subsidiaries, enjoyed a meteoric rise after its founding in 2007, and was valued at $500 million in 2013 under Tham's stewardship.

But after Tham was arrested in 2014, most bank branches shut and the State Bank of Vietnam, the central bank, acquired Ocean Bank for $0.

Ocean Group is still active in real estate and hotels and services and was valued at about $3.5 million in 2016, according to its website.

Vietnam has already jailed dozens of bankers in other high-profile banking cases, which some see as a commitment to cleaning up the sector.

"(Monday's) trial shows progress made by the Vietnamese government in the fight against corruption," Nguyen Hoang Hai, deputy chairman of the Association of Financial Investors, told AFP.

In September last year 36 former Vietnam Construction Bank employees were given jail terms of up to 30 years, after they were accused of secretly withdrawing millions of dollars from clients' accounts to use for loans or keep for themselves.

Bad debts have long plagued the banking industry. They make up some eight percent of outstanding loans, according to the state bank, though experts say the real number could be far higher.