More than half a million young people could need emergency assistance - including food packages - as a direct result of an Abbott government change which welfare groups have warned will lead to ''catastrophe''.

In an admission that a mandatory six-month wait for benefits for those under 30 is likely to push hundreds of thousands of people into crisis, officials have told Senate hearings the government had allocated $230 million over four years to provide emergency relief to those affected.

The government expects 550,000 applications for assistance, which will be delivered by charities in the form of food vouchers, transport or medications, household goods, clothing or by helping to pay rent or utility bills. Department of Social Services deputy secretary Serena Wilson admitted in a Senate hearing on Wednesday there was a risk that some affected by the change would become homeless.