Prime Minister Malcolm Turnbull and Opposition Leader Bill Shorten have gone head to head in their first official debate at the National Press Club in Canberra, arguing on company tax cuts, climate change, health and asylum seekers.

The leaders were grilled by three senior political journalists in the hour-long debate, in contrast to the town hall-style people's forum held in western Sydney earlier this month.

Their performances were widely regarded as lacklustre on social media.

Mr Turnbull opened the debate pitching his national economic plan.

"These are times of enormous opportunity and uncertainty, these are times of great challenge," Mr Turnbull said.

"These are times when we need a clear economic plan."

Opposition Leader Bill 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.

He said Labor's plans would "ensure jobs, education and Medicare".

Both leaders were asked how they could be trusted by voters following the unceremonious dumping of leaders in recent years.

Political editor of the Australian Financial Review, Laura Tingle asked Mr Turnbull whether he had abandoned things he believed in and whether the nation would see a different Malcolm Turnbull if he was given his own mandate.

Mr Turnbull said he was a "well-known quantity in Australian public life".

"I did not come into this role as a political activist," he said. "I did not come in here as a political staffer."

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

Mr Shorten said 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.

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.

CLIMATE CHANGE

Asked about climate change and his former support for emissions trading, Mr Turnbull said Australia was playing its part.

"I stand where I have always stood, recognising that we must take action as a global community to reduce our greenhouse gas emissions to protect our environment for our children, our grandchildren and the generations that come thereafter," Mr Turnbull said.

Mr Shorten said the prime minister was "Tony Abbott lite" when it came to tackling climate change.

"Malcolm, whatever happened to the old Malcolm Turnbull on climate change? You were so impressive when you were leading on climate change. Now you're just implementing Tony Abbott's policies," Mr Shorten said.

"There's a big difference between me and Mr Turnbull - I genuinely lead my party whereas your party genuinely leads you."

Mr Turnbull said it was "another cheap shot".

Environment protesters gave the leaders a noisy welcome as they arrived for their head-to-head campaign debate.

About a dozen people holding signs calling for action on climate change and the Great Barrier Reef stood outside as the leaders arrived 30 minutes before the debate.

COMPANY TAX CUTS

Labor will block the coalition's proposed corporate tax cuts in the Senate if the government is returned to power on July 2.

"I have to say that when it comes to corporate tax cuts Labor doesn't think they're the right idea for this nation - full stop," Mr Shorten said.

He said the government's $50 billion tax cut plan was a "very expensive risk", which mirrored the economic strategies of Margaret Thatcher and Ronald Reagan.

Mr Turnbull said former Labor treasurer Paul Keating cut company tax to boost the economy.

"Why did he do that? ... For every dollar cut from company tax you get $3 going to labour - the employees - and $4 additional value in GDP," Mr Turnbull said.

"We are lowering taxes on investment so we get more investment."

HEALTH

Mr Shorten promised to boost hospitals funding by a "significant dimension".

But the opposition leader declined to say whether a Labor government would restore all of the Commonwealth health funding cut from the states in the controversial 2014 budget.

"When it comes to our hospitals policy, we won't announce our whole policy platform tonight ... but what I can promise Australians right here, right now, is we will put more funding into hospitals than Mr Turnbull has promised by some significant dimension."

ASYLUM SEEKERS

Mr Turnbull said people smugglers were telling their customers if Labor was elected "it'll be all on again", after declaring he could "rule out any of the detainees coming to Australia".

"The reality is we have to be very firm about this. We do no favours to anybody by being weak on border protection in the way Labor was."

He said Labor was a party divided on asylum seeker policy.

"He claims to be on a unity ticket with me but his party is not," Mr Turnbull said of the opposition leader.

Mr Shorten said Mr Turnbull was "playing with fire" with the remarks as he had conceded people smugglers were "watching every nuance in the debate".

"Shame on you for giving the people smugglers any hope that they could be back in business," he said to Mr Turnbull.

"Labor has the same approach as the government when it comes to deterring and defeating the people smugglers."

Mr Turnbull was criticised on social media for referring to his upbringing.

"I was brought up by a single dad who didn't have much money. And he struggled to send me to school, and I had some really charismatic teachers that transformed my life."

Mr Shorten said he was a person who "stood up for the fair go my whole working life. I'm a person who has been in the workplaces of Australia standing up for people."