The Australian Tax Office is stepping up its surveillance of Australians funnelling money into secret offshore bank accounts.

The extra scrutiny is part of an amnesty program that will allow some tax dodgers to avoid severe punishment by declaring income and agreeing to come back into the tax system before December 2014.

The agency will issue please explain notices to wealthy Australians or banks it suspects of facilitating tax avoidance over the coming months.

Around 160 individuals have already come forward as part of the amnesty program, called Project Do-It, netting the government around $13 million in lost tax revenue. A further 1700 international audits and reviews are under way.

Assistant commissioner David Allen said the Tax Office had improved its ability to track individual fund transfers through data collected by Austrac.

''What it is showing us, probably for the first time, is the huge number of offshore accounts in existence and the different modes of getting money offshore,'' he said.

The ATO is focusing its efforts on money flowing into accounts in six key jurisdictions: Switzerland, Israel, Liechtenstein, the Netherlands, South Africa and Hong Kong.

As well as the 160 people who have come forward, a further 250 have made expressions of interest in declaring their accounts.

The ATO receives transaction data from Austrac each day that allows it to track individual money flows to offshore accounts almost as they happen.

''We're able to much better pinpoint where these funds are [going],'' Mr Allen said.

The agency will allow those who co-operate with the Tax Office to be part of its amnesty for the rich - those with wealth of $30 million or more. The amnesty comes ahead of a number of changes to the tax system, as well as a new treaty between Australia and Switzerland, which would give the ATO greater access to secret bank account information.

Mr Allen said the ATO had visited banks in Australia to remind them of the treaty and new OECD reporting standards.

''We're seeing some financial institutions being quite proactive and actually writing to customers who they think might be affected by these changes,'' he said.

Australia is leading discussions about tax avoidance and profit shifting as part of its role chairing the G20 meetings in Brisbane later this year.