DEAD Aussie expats have been sent taxpayer-funded welfare cheques, a government department admits.

Centrelink is cracking down on social security overpayments to Australians living overseas, including "payments that may have continued after the person has died'', the Department of Human Services reveals in its 2013 annual report.

But the department could not provide details yesterday of how much it had paid the dead Aussie expatriates - or whether it had recovered the money.

New official data reveals a record 2 million Australians racked up $1.8 billion worth of debts with Centrelink during 2012/13, through fraud and accidental over-claiming of pensions and family benefits.

Debt collectors were used to recover 10 per cent of the $1.2 billion which Centrelink managed to recoup.

Centrelink fielded more than 105,000 fraud tip-offs during the year - half through a dob-in phone line.

And it used data-matching with eBay to nab welfare recipients who failed to declare cash income from online auctions.

The number of fraud "interventions'' has almost halved, from 1.9 million in 2011/12 to 866,597 in 2012/13.

A Human Services spokeswoman said the department was "being pro-active in trying to prevent debts before they happen''.

Through this approach, we remind people of their obligations so they don't unintentionally accrue a debt, but also identify cases of serious, deliberate fraud,'' she said.

"This allows us to focus investigation resources on the more serious cases of fraud and helps protect the integrity of the welfare system."

But the government's welfare agency is spying on fewer fraud suspects - more than halving its optical surveillance from 337 cases in 2011/12 to just 143 last financial year.

The Child Support Agency swooped on 170,000 parents who refused to pay child support to their former partners, by docking the debts from their wages or tax refunds.

Fathers account for 92 per cent of parents who have to pay child support.

Hundreds of "deadbeat dads'' were blocked from leaving Australia for holidays or migration, until they coughed up the cash for child support payments.

The Human Services report shows "departure prohibition orders'' were used 461 times to recover $6.7m in payments during 2012/13.

Terese Edwards, chief executive of the National Council of Single Mothers and their Children, said lone mums were going without food because fathers refused to contribute to the cost of raising their children.

"Refusing to pay child support is rendering your children to hardship,'' she said.

"The cornerstone of the child support scheme is that the biological parents are financially responsible for their children - full stop.''

Ms Edwards said single parents did not qualify for full welfare payments until they lodged a claim for child support.

She said one mother who contacted her recently had not eaten for two days and was "four days out of moving out of her home'', because her ex-partner had not paid any child support and she could not afford food or rent.