A huge leak of 11.5 million documents from a Panama law firm reveals how the world's rich, including Russian President Vladimir Putin and other political leaders, hide their money, a German newspaper says.

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The leak comes from Panama-based Mossack Fonseca, one of the world's most secretive offshore law firms.

The firm said it had never been charged for criminal wrongdoing in its efforts to help clients launder money, dodge tax and circumvent financial sanctions.

The documents, dubbed the Panama Papers, were obtained by Sueddeutsche Zeitung, a daily newspaper headquartered in Munich.

Sueddeutsche said an employee at the law firm had leaked the data, telling the newspaper he risked his life in doing so. The employee was not identified in the report.

The newspaper shared the Panama Papers with the Washington-based International Consortium of Investigative Journalists (ICIJ) and other news outlets, including the BBC and The Guardian.

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Some 370 journalists in 78 countries were involved in evaluating the data dump.

"2.6 terabytes of data, 11.5 millions documents, and 214,000 shell companies: The Panama Papers are the largest data leak journalists have ever worked with," Sueddeutsche tweeted on Sunday.

The documents link at least 12 current and former heads of state and 128 other politicians to illicit financial transactions. Those implicated include longtime Egyptian autocrat Hosny Mubarak and Syrian President Bashar al-Assad.

The most widely circulated revelations from the Panama Papers shed light on the financial transactions that have contributed to the wealth of members of Putin's inner circle.

The BBC reported that the data reveals the existence of a money laundering ring involving the Russian leader's closest associates and Bank Rossiya, a financial institution subjected to EU and US sanctions in the wake of Moscow's annexation of Crimea.