The prime minister says data clearly shows the pandemic has hit women and young people the hardest.

And Mr Morrison said employers who sack older workers to hire younger ones won't get the government subsidies.

"The subsidy only applies for new places over and above what your current level of employment is," he told the Seven Network on Wednesday.

"If they drop the level of employment to take on other workers, they won't get the subsidy. It's got to be new jobs over and above what is there now."

Tuesday night's economic blueprint outlined a $4 billion program offering all businesses - excluding the four big banks - credit to hire young job seekers.

Workers under 30 will draw a $200 weekly government subsidy, while someone between 30 and 35 will attract $100.

Newly-hired staff must work at least 20 hours a week.

Labor argues 928,000 people out of work aged over 35 will be excluded from the scheme.

"Too many people have been left out and left behind," shadow treasurer Jim Chalmers told the ABC.

Treasurer Josh Frydenberg argues the scheme is designed to drive down unemployment, with 450,000 jobs tipped to be created.

"We settled on 35, because young people have been particularly impacted by this crisis," he told the ABC.

Unions want a guarantee the money will end up in workers' pockets.

"We need safeguards to prevent businesses using government investment to increase executive pay, bonuses or payoffs to shareholders," ACTU president Michele O'Neil said.

Australian Industry Group chief executive Innes Willox said the subsidies along with support for 100,000 apprentices were important.

"These are measures targeted to younger Australians that we know from experience are among the most at risk in the wake of an economic downturn," he said.

JobKeeper wage subsidies will end at the end of March after being tapered off.

The big-spending budget will also provide a tax cut for more than 11 million Australians.

Low and middle-income earners will receive relief of up to $2745 for singles and $5490 for couples compared to 2017/18.

Tax cuts will be backdated to July 1, with the 32.5 per cent threshold lifted from $90,000 to $120,000 and the 19 per cent trigger hiked from $37,000 to $45,000.

Labor is critical of a lack of assistance for aged care or social housing.

The budget papers revealed an eye-watering deficit of $213.7 billion which is predicted to fall to $66.9 billion in 2023/24.

Government gross debt will exceed $1 trillion by 2021/22, equating to 50.5 per cent of gross domestic product.

Australian Associated Press