Bill Shorten and Malcolm Turnbull have fended off questions about their trustworthiness and ability to deliver on their pledges after the election.

Entering the fourth week of a gruelling eight-week election campaign, the Prime Minister and Opposition Leader gave lacklustre performances at the first formal leaders’ debate on Sunday night.

Mr Turnbull ousted Tony Abbott in September to become PM, while Mr Shorten played a role in dumping Kevin Rudd and Julia Gillard.

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The Prime Minister answered the question on trust saying he was a “well-known quantity in Australian public life”.

“I did not come into this role as a political activist,” he said.

“I came into this role as an adult, at 50, after a lifetime of working and building businesses.”

Mr Shorten took the question head-on, saying Labor had learned its lesson from the “difficult period” of leadership change.

“We have demonstrated more unity of purpose than we have in a very long time,” he said.

Asked whether they would respect each other’s mandates should the other party win, Mr Turnbull said it was impossible to know what a Labor government would deliver because it backflipped on policies such as restoring the Schoolkids Bonus.

Opposition Leader Bill Shorten. Photo: ABC

Mr Shorten said Labor would not support the Coalition’s $50 billion corporate tax cut plan, meaning the Coalition would need crossbench support or a Senate majority to get its key economic policy through parliament.

The debate got heated when the prime minister suggested people smugglers would use a Labor government as a “marketing opportunity” to get back into business.

“Shame on you,” Mr Shorten said.

The Labor leader described Mr Turnbull as “Tony Abbott lite” when it came to tackling climate change, given the prime minister had walked away from his previous support for an emissions trading scheme.

“There’s a big difference between me and Mr Turnbull – I genuinely lead my party whereas your party genuinely leads you,” Mr Shorten said.

Mr Turnbull said it was “another cheap shot”.

In his opening statement, Mr Turnbull said it was a time of enormous opportunity and uncertainty, which needed a “clear economic plan”.

Mr Shorten said the election was about the next 10 to 20 years.

“This election is about … Labor’s positive plans for a strong economy and a fair society,” he said.

Both leaders announced sports programs on Sunday before heading into the National Press Club for the debate.

-AAP