Up to six Government departments face investigation in the hunt for the sources of leaked Cabinet papers.

State Services Commissioner Ian Rennie yesterday announced investigations into the leaking of the two papers detailing mining and public service restructuring plans.

The Herald understands they were made public before the Cabinet saw them.

The scrutiny, which the Opposition is calling "a witch hunt", is likely to cover the Department of Conservation, the Ministry of Economic Development, the Ministry for the Environment, Internal Affairs, the Treasury and the Department of the Prime Minister and Cabinet.

The two separate inquiries have been started at the request of State Services Minister Tony Ryall after Cabinet discussions.

The Government has not commented on the accuracy of the information leaked.

Forest and Bird advocacy manager Kevin Hackwell declined to reveal how he obtained information on the Government's plans to widen the hunt for minerals on Department of Conservation land.

And he doubted the investigation would uncover his source.

"When you get a policy development getting as far as a Cabinet paper, an awful lot of people, and not just in the bureaucracy - even outside of State Services, you've got people in and around Cabinet and in the Beehive - a lot of people get access to that information.

"An awful lot of New Zealanders are very concerned about what was being proposed, so it's hardly surprising that someone in that large group would be concerned enough to make it publicly available."

Mr Ryall said any potential breach of security in the public or the private sectors was "always investigated and procedures are reviewed and that's what's happening here".

When it was pointed out he had frequently leaked information to the media when in Opposition, Mr Ryall said he would never have disclosed his sources.

"But I have to say I don't think we had very many coming from the public service at all, and when the previous Government was in a similar position, there were these standard investigations just to see if there was a breach."

But State Services Commission investigations into leaks are rare.

The last was in 2007, after the premature release of Cabinet documents on plans to split Telecom.