Mr Morrison cleared the way for a five-week campaign by visiting Governor-General Sir Peter Cosgrove in Canberra just before 7am on Thursday to set the polling date and seek the dissolution of Parliament.

The decision gives Australians about one week to enrol to vote or update their enrolments at the Australian Electoral Commission.

Mr Morrison launches the campaign with a message to Australians to vote for a "strong economy and strong budget" by backing the Liberals and Nationals.

Opposition Leader Bill Shorten has urged voters to remove the government after "six years of instability" including three prime ministers.

The Coalition goes into the campaign behind Labor in the opinion polls and the betting markets after two terms in office under Tony Abbott, Malcolm Turnbull and Mr Morrison.

Labor has held a lead over the Coalition in the polls for more than two and a half years, with this week's Ipsos survey putting it ahead by 53 to 47 per cent in two-party terms.

While the government won 76 seats at the last election and held a narrow majority through much of the last term, it lost the seat of Wentworth after Mr Turnbull resigned and lost another member when Julia Banks quit the Liberals to sit as an independent.

ABC election analyst Antony Green estimates the government goes to the election with 73 seats following a redistribution in Victoria.

Mr Green estimates Labor has 72 seats as a result of the redistribution, a significant gain on the 69 seats it won at the last election. There are six independents seeking re-election.

The House of Representatives has been increased from 150 to 151 seats since the last election.

Mr Morrison visited Yarralumla for a brief meeting with Sir Peter in Canberra to ask that Parliament be dissolved and the writs be issued for the May 18 polling day.

The writs for the election could be issued on Friday, in line with the timetable for earlier elections, in the formal commencement of the caretaker conventions for the public service.

Australians are likely to have about one week to enrol to vote or update their enrolments.

Early voting opens about two weeks after the writs are issued.

The Australian Electoral Commission said several hundred thousand people updated their details on the electoral roll in the week before the rolls closed at the last election.

It will be mandatory for all candidates to submit material to the AEC to show they have renounced any right to foreign citizenship, although the commission will not vet this information.

AEC spokesman Phil Diak said there was a growing trend towards voters casting their ballots ahead of polling day, with about four million of these postal and pre-poll votes at the last election.

- SMH/The Age.