The Tax Office is investigating more than 800 high net wealth Australian clients of the controversial Panama law firm Mossack Fonseca, which is the focus of an unprecedented leak of tax haven records released globally.

More than 11.5 million documents have been leaked from Mossack Fonseca's files, revealing the secrets of hundreds of thousands of clients – including several thousand Australians – covering a period over almost 40 years, from 1977 until as recently as last December.