Prime Minister Scott Morrison will call the federal election on Thursday after returning to Canberra to announce May 18 as the date when Australians will go to the polls.

Mr Morrison arranged to fly from Melbourne to Canberra late on Wednesday in order to be ready to see the Governor-General, Sir Peter Cosgrove, early on Thursday morning to ask that Parliament be dissolved.

Prime Minister Scott Morrison will likely call the election for May 18. Credit:Alex Ellinghausen

Public servants are preparing to enter caretaker mode on Friday night.

The Coalition cleared the way for the announcement by making another round of appointments to government posts on Wednesday afternoon, with former Liberal Party president and cabinet minister Richard Alston one of the winners.