The Greens in Australia now look likely to hold the balance of power in the Senate and assume a possible kingmaking role in the House of Representatives.
Greens leader Bob Brown dubbed the party's result, which saw it garner more than 11% of the vote nationally on Saturday, as a "Greenslide".
Senator Brown said the Greens were now the undisputed third Australian political party.
"We will use this vote from the Australian people responsibly. We will use it to give this nation leadership. We will use it to innovate. We will use it to educate," he said.
"On a vote-for-vote basis, the Greens on 12% would be having 17 seats in the Lower House, and it's time we moved to proportional representation in this country."
The ABC reports a hung parliament would be the first in Australia since 1940, when United Australia Party of Robert Menzies governed with the help of the Country Party and two independents.
First seat in general election
The Greens claimed their first victory in the House of Representatives in a general election, with Adam Bandt taking the seat of retiring finance minister Lindsay Tanner in Melbourne.
(Another Green MP won a by-election in New South Wales in 2002).
The ABC reports Mr Bandt needed a swing of 4.7% to win but extended that to more than 10% on a two-party preferred basis.
Mr Bandt says he will not help Opposition Leader Tony Abbot form a Government. He says the two major parties have let voters down.
However, Senator Brown says the Greens will act responsibly if they take the balance of power.
"Whether it's an Abbott government or a Gillard government we will work with that government, that's what the people will have voted for," he said.