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.