Anthony Albanese will lead a ‘yes’ campaign blitz across the country while a former leader has warned against signing a “blank cheque” in the constitution as the voice referendum nears its crescendo.

The prime minister was joined by his son on Saturday as he cast an early vote in the referendum in his Sydney electorate of Marrickville before outlining the busy schedule he had planned for the final week of the campaign.

“I was in Queensland (on Friday),” he said.

“I will be in the other five states and two territories over the coming seven days.”

Mr Albanese appealed to voters to see through the fears projected by the ‘no’ side.

He said Australians were optimistic and hopeful.

“What lifts a nation up is hope and optimism and a vision for the future moving forward,” he said.

“When people wake up on October 15, and the sky is still there – there is nothing to fear from a ‘yes’ vote – we will feel better about ourselves.

“The burden of colonialism that sits on our shoulders will be lifted off a little bit by recognising first Australians in our nation’s founding document.”

Former prime minister Tony Abbott, who fronted the media alongside two federal opposition MPs on Saturday, urged voters to reject the proposal, calling the voice “a huge leap into the constitutional dark”.

The ex-Liberal leader likened the change to signing a blank cheque in the constitution.

Tony Abbott says the voice would “entrench disunity and inequality in our constitution”.

“Unless you are absolutely sure that this is change for the better, and unless you are absolutely sure that you are comfortable with all the possible ramifications, you should vote no,” Mr Abbott said.

“People are determined, by and large, to vote yes for unity and yes for equality, rather than voting yes to this extremely divisive voice, which would entrench disunity and inequality in our constitution.”

Australians are being asked whether they want to put an Indigenous advisory body called the voice into the constitution.

It would be a permanent body but hold no veto right and the parliament would have the power to change the model and how it functioned through legislation.

Australians will vote on the proposal on October 14, with a majority of people in at least four states required to vote ‘yes’ for the referendum to be carried, as well as a majority of Australians nationally.

—AAP