The leak of two million emails and other documents, mostly from the offshore haven of the British Virgin Islands is expected to cause global shockwaves.
An estimated $32 trillion (€25 trillion) is locked up in the accounts, which are used by plutocrats, heads of state, and celebrities to avoid paying income tax.
The revelations come shortly after the resignation of the French Finance Minister Jérôme Cahuzac on 19 March, apparently over a secret bank account he held in Switzerland. Jean-Jacques Augier, President François Hollande's campaign co-treasurer and close friend, has also been forced to publicly identify a Chinese business partner.
Mongolia's former finance minister and deputy speaker of its parliament has reportedly said that he may have to resign from politics as a result of the investigation.
In Belgium, a first batch of revelations is expected later today on the website of the daily Le Soir.
According to initial information, the leak has enabled investigators to trace the “disappeared” fortunes of dictators, such as Ferdinand Marcos in the Philippines and Robert Mugabe in Zimbabwe.
The Guardian, the BCC and other international media will jointly publish the results of their investigations over the course of the week. According to the Guardian newspaper, the investgative project could prove extremely damaging for confidence in tax havens, used by the world's wealthiest people.
Activity by an extraordinary array of government officials and rich families across the world has been identified, from the UK, Canada, the US, India, Pakistan, Indonesia, Iran, China, Thailand and former communist states.