Police raided HSBC's Switzerland office in Geneva this morning.
Swiss prosecutors confirmed it is investigating "HSBC Private Bank (Suisse) SA and persons unknown for suspected aggravated money laundering".
In a statement, Swiss prosecutors said its probe into the troubled bank could be extended to "people suspected of committing or participating in money laundering."
"A search is currently underway in the premises of the bank, led by Attorney General Olivier Jornot and the prosecutor Yves Bertossa," said Geneva's prosecutor in an emailed statement to Business Insider.
HSBC is alleged to have repeatedly helped its richest clients hide and dodge taxes in their home countries. The allegations stem from the largest financial data leak of its kind in history.
Around 140 journalists from 45 different countries helped unearth the secret accounts in Switzerland after Herve Falciani, an HSBC whistleblower turned employee, leaked it to French authorities.
Regulators in Belgium, France, Argentina, the US and Switzerland said they would individually consider examining 100,000 of HSBC’s clients’ accounts in a bid to root about mass tax avoidance.
However, today's raid centres on money laundering.
HSBC was already fined £1.2 billion in December 2012 for failing to prevent money laundering of criminal cash.
The US Department of Justice said that the bank also failed to carry out its due diligence on certain bank accounts.
At the time, authorities also said that HSBC violated sanctions laws by doing business with Iran, Libya, Sudan, Burma and Cuba.
HSBC apologised for its conduct and said it has strengthened its controls since then. However, US authorities warned that it could reopen the money laundering investigation from three years ago, following the tax evasion data leak.
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