"Who do you trust?" he asked aloud after announcing a May 18 election.

John Howard must have been impressed - he uttered those very same words 15 years ago.

This time around, the prime minister's pitch to voters was crystal clear.

He alone could be trusted to build the economy and make people's lives easier in the years ahead.

But Labor is urging voters to cast an eye backwards as they prepare to cast their votes.

To look at six years of coalition chaos and confusion - dysfunction and division - with three Liberal leaders having been at the helm.

Opposition Leader Bill Shorten is demanding political stability, declaring he alone can deliver it.

There was a sense of relief above all else when Morrison finally fired the starter's gun on a five-week campaign.

Reporters and cameramen, political staffers and boffins, huddled together in Canberra's early morning cold.

Itching to get the show on the road, their bags have been packed for weeks.

Personalities are bound to play a major part in the upcoming federal poll.

Staring straight down the barrel of the television camera lenses, Morrison reminded voters of a binary choice.

"It is a choice between me as prime minister and Bill Shorten as prime minister," he said, offering a penetrating glimpse of the bleeding obvious.

"You vote for me, you'll get me. You vote for Bill Shorten and you'll get Bill Shorten."

Howard ran a successful campaign on trust in 2004, but stumbled and fell three years later when he vowed to "go for growth".

Morrison knows that this time around, economic growth alone won't get him over the line.

Voters need to know why it matters.

And so off he went about investment in health, new medicines and education.

Money for defence, and national security, and the social safety net.

"Who do you trust to deliver that strong economy which your essential services rely on?" Morrison posited.

"Who do you trust to deliver the strong economy and the budget management that these services can be funded, that the business that you work for will be there in three years, in five years, in 10 years?"

Morrison, seven months into the country's top job, spoke of an agenda not yet complete.

"There is more to do and a lot has got done, and we are getting on together with the job," he said.

Standing in the backyard of a suburban Melbourne home, Shorten struck a different tone.

He spoke of an agenda six years in the making.

The government was tired, and divided, and stuck in the past.

His team was strong and united, full of beans, and ready to govern for ordinary Aussies.

"My feet are firmly planted in the backyard of a Mitcham house because I understand that politics should be about the people," Shorten told reporters.

"It's about cost of living, education, health, good jobs and renewable energy."

As Shorten presented his pitch to voters, a Liberal Party truck did laps of the street outside.

"THE BILL AUSTRALIA CAN'T AFFORD" screamed the slogan on wheels.

As he called curtains on his own press conference, the prime minister issued a similar warning about his opposite number.

"It's taken us more than five years to turn around Labor's budget mess. Now is not the time to turn back," Morrison said.

For his part, Shorten argued Australia could scarcely afford not to change tack.

He acknowledged many Australians thought the system was broken, with everyone in it for themselves.

"If you want a government who is united and not constantly trying to tear each other down, then vote Labor on May 18," he said.

At least the leaders can agree on one thing: this election, like every one before it, is about trust.

Australian Associated Press