SYDNEY/WELLINGTON, April 4 -- The Australian Tax Office (ATO) said on Monday it is investigating more than 800 wealthy clients of a Panama law firm for possible tax evasion.

The probe follows the reported leak of more than 11.5 million documents from the files of law firm Mossack Fonseca, based in the tax haven of Panama, revealing details of hundreds of thousands of clients.

The documents are at the center of an investigation published on Sunday by the International Consortium of Investigative Journalists, the German newspaper Süddeutsche Zeitung and more than 100 other news organizations around the globe. ICIJ is the international arm of the Center for Public Integrity.

The leaked "Panama Papers" cover a period over almost 40 years, from 1977 until as recently as last December, and allegedly show that some companies domiciled in tax havens were being used for suspected money laundering, arms and drug deals, and tax avoidance.

"Currently we have identified over 800 individual taxpayers and we have now linked over 120 of them to an associate offshore service provider located in Hong Kong," the Australian tax office said in a statement emailed to Reuters. It did not name the Hong Kong company.

ATO Deputy Commissioner Michael Cranston said his office was working with the Australian Federal Police, the Australian Crime Commission and anti-money laundering regulator AUSTRAC to further cross-check the data from the documents.

"Some cases may be referred to the Serious Financial Crime Taskforce," Cranston said in the statement. "The message is clear - taxpayers can't rely on these secret arrangements being kept secret and we will act on any information that is provided to us."

Treasurer Scott Morrison told ABC Radio Monday that "our record when it comes to tax avoidance and particularly multinational tax avoidance is one of legislation and action."

The 800 individuals under investigation include some taxpayers who had previously been investigated and others who had reported themselves to the tax office under its so-called Project DO IT - Disclose Offshore Income Today. The voluntary disclosure initiative, which closed at the end of 2014, allowed people to come forward and avoid steep penalties and criminal charges.

However, the tax office said the individuals under investigation also include "a large number of taxpayers who haven't previously come forward."

In New Zealand, the tax agency is "working closely" with its tax treaty partners to obtain full details of any New Zealand tax residents who may have been involved in arrangements facilitated by Mossack Fonseca, said John Nash, Inland Revenue's international revenue strategy manager, in comments emailed to Reuters.

Nash said there is an "active compliance programme focused on those who engage in abusive offshore arrangements and don't meet their tax obligations."

He urged any New Zealand tax residents who may have been involved in offshore arrangements that do not comply with tax laws to come forward voluntarily "rather than face more severe action later should we identify participation in tax evasion or avoidance."