A top UN official has delivered a scathing assessment of Australia's welfare policies describing them as 'punitive' and harmful to women.

Australian Philip Alston is the UN's Special Rapporteur on Extreme Poverty. He accuses the government of pursuing policies that 'stigmatise' and 'marginalise' poorer sections of society.

In a letter sent to the government this week, Philip raised concerns about the planned expansion of cashless welfare cards, and their impact on indigenous communities.