Share price of HSBC,a leading itnernational bank, fell to its lowest level since 1995 amid allegations of money laundering, a BBC report said.
In 2013 and 2014 the bank allowed fraudsters to transfer millions of dollars around the world even after it had learned of their scam, leaked secret files show, the report said.
HSBC says it has always met its legal duties on reporting such activity.
On Monday in Hong Kong, the shares fell by more than 4% to less than HK$30. In London at midday they were down 6%.
The UK-based bank is currently facing multiple pressures including political tension in Hong Kong and the pandemic fallout.
Although HSBC is headquartered in London, more than half of its profits come from Asia and its shares are important components of both the London and Hong Kong share markets.
Shares in rival banks have also been hit. At lunchtime, Standard Chartered and Barclays were down by 5% and 6% respectively, while Germany's Deutsche Bank was down 8%, BBC said.
HSBC had been under pressure on multiple fronts before the files were leaked and its shares have taken a particularly hard battering this year, falling by some 50%.
Its role in a $80 million fraud is detailed in a leak of documents - banks' "suspicious activity reports" - that have been called the FinCEN Files.
HSBC moved the money through its US business to HSBC accounts in Hong Kong in 2013 and 2014, the papers alleged.