A Swiss international aircraft flies past the HSBC headquarters building in the Canary Wharf financial district in east London.

Swiss authorities yesterday raided the offices of British banking giant HSBC's Swiss unit as part of a money laundering probe into the bank that has been accused of helping clients to dodge millions of dollars in taxes.

The investigation comes just days after HSBC Switzerland found itself at the centre of a global scandal following publication of secret documents claiming it assisted many of its wealthy clientele in thwarting the taxman.

"A search is currently under way in the bank's offices," Geneva's top prosecutors said in a statement.

The search and money laundering investigation were launched "following the recent revelations related to HSBC Private Bank (Switzerland)," they added.

The cache of files, made public in the so-called SwissLeaks case, claimed HSBC's Swiss private banking arm helped clients in more than 200 countries evade taxes on accounts containing $119 billion (104 billion euros).

The files provided details on over 100,000 HSBC clients, including people targeted by US sanctions, suspected arms dealers and drug traffickers.

A wide range of celebrities, politicians and business leaders were also named in the files, although their inclusion does not necessarily imply wrongdoing.

The documents, which were originally stolen by former HSBC IT worker Herve Falciani in 2007, alleged that billions of dollars transited through the bank as customers from around the world tried to dodge the taxman in their home countries or laundered dodgy proceeds through offshore shell corporations.

According to Swiss law, a bank can be held responsible for "aggravated money laundering" if it does not take all the necessary measures to ensure such infractions do not take place within its institution.

Geneva cantonal prosecutor general Olivier Jornot and another top prosecutor, Yves Bertossa, were heading the search and probe against HSBC.

They said the probe initially only targeted the bank itself, but warned that "depending on the evolution, the investigation might be broadened to include physical persons suspected of committing or participating in acts of money laundering."

Anyone found guilty of such crimes could face up to five years behind bars as well as large fines, Geneva judicial authorities told AFP.

Following the SwissLeaks revelations, HSBC's Swiss banking arm insisted it has undergone a "radical transformation" since the period referred to in the files.

HSBC now has "strong compliance controls in place", Franco Morra, the head of HSBC's Swiss unit, told AFP in an email, adding that the revelations are "a reminder that the old business model of Swiss private banking is no longer acceptable".

The SwissLeaks documents were obtained by French newspaper Le Monde and shared via the International Consortium of Investigative Journalists with more than 45 media organisations worldwide.

As soon as the documents were made public on February 9, calls arose for a Swiss probe against HSBC Switzerland, which is already facing prosecution in the United States, France, Argentina, Spain and Belgium. Switzerland had so far only launched an investigation against Falciani.

Falciani himself said last week that the media reports on the documents' contents were based on just a fraction of the files he handed over to French authorities.

"This is only the tip of the iceberg," the 43-year-old Franco-Italian told France's Le Parisien newspaper.

Dubbed the "Snowden of tax evasion" and "the man who terrifies the rich", Falciani remains wanted on data theft charges, but France and Spain have offered him protection by refusing to extradite him to Switzerland.