The polls have opened in South Australia and Tasmania as the last two states with Labor governments make a decision on who will govern for the next four years.

In South Australia, about one million people set to cast their votes to determine who will govern the state for the next four years.

Premier Jay Weatherill is seeking a fourth term for his Labor administration while Liberal leader Steven Marshall is trying to end 12 years of Labor rule.

The opposition needs a uniform swing of about three per cent to pick up the six seats it needs to govern in its own right.

The Liberals currently hold 18 seats in the 47-seat House of Assembly with Labor on 26 and three held by independents.

Tasmanian Liberal leader Will Hodgman. Photo: AAP

A hung parliament is a possibility with latest polling suggesting Labor is holding on in some key marginal electorates.

Mr Marshall has not ruled out leading a minority government while Mr Weatherill says he remains focused on winning enough seats for Labor to continue to hold power.

The electoral commission says 1,142,419 South Australians are enrolled to vote while about 70,000 of those have already cast their ballots at early voting centres in the lead-up to the election.

About 86,000 people are also expected to lodge postal votes.

More than 360,000 Tasmanians will vote in 305 polling places as far flung as King Island in Bass Strait.

Voters will elect a 25-seat House of Assembly, with the state’s Hare-Clark system delivering five members from each electorate.

They will form the state’s 48th parliament.

Seven parties will field 126 candidates across the state’s five electorates – Bass, Braddon, Denison, Franklin and Lyons.

Voting closes at 6pm (AEDT).