Prime Minister Tony Abbott has told global leaders they bear heavy responsibility to achieve change ahead of the G20 summit’s formal opening.

Mr Abbott was speaking at Queensland Parliament House where he is hosting the G20 leaders at a retreat and barbecue lunch before the summit kicks off on Saturday afternoon.

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Those assembled included US President Barack Obama and Russian President Vladimir Putin.

“Nowhere on earth will there be a more influential gathering than this,” he told the group.

But he reminded leaders they bore heavy responsibility to achieve economic change at the summit.

“The world is looking to all of us right now to try to demonstrate to an uncertain and at times anxious world there are people who know what they are doing, that there are people who have a plan … for growth and for jobs,” Mr Abbott said.

“That’s our challenge, to leave this G20 meeting in 48 hours’ time having instilled more confidence in the people of the world that there is a better and brighter future for all of us.”

However, Mr Abbott acknowledged there were limitations in what could be achieved, and that there would be inevitable disagreements among the leaders.

He urged them to speak candidly and openly at the summit.

“The only rules, as far as I’m concerned, are if we can speak from our heart rather than from a script, that would be good.”

He cited his own difficulties with the budget – particularly in gaining support for proposed higher education changes and the $7 GP co-payment – as examples of the need to persist with important reforms.

Opposition Leader Bill Shorten labelled the prime minister’s remarks “weird and graceless”.

It was a missed opportunity to promote Australia’s position as a global leader, he said.

“This was Tony Abbott’s moment in front of the most important and influential leaders in the world and he’s whingeing that Australians don’t want his GP tax,” Mr Shorten said in a statement to AAP.