South Australian Labor Senator Don Farrell has conceded it would take a "minor miracle" for him to be re-elected after a major swing against the ALP in the state's Senate vote.
With more than 70 per cent of the ballots counted, Independent Senator Nick Xenophon's group has won more than 25 per cent, almost certainly ending the Labor Party powerbroker's hopes for re-election.
The Greens' Sarah Hanson-Young and Family First's Bob Day could also claim spots alongside Labor's Penny Wong and the Liberals' Cory Bernardi and Simon Birmingham.
Senator Farrell on the Labor ticket in October last year after pressure for Senator Wong to take up the position.
He says it was the right decision at the time and has no regrets.
"I'm a person who likes to look forward rather than back. We've had to make some tough decisions over this period of time," he said.
"The party has been very divided in the past. We need to reunite now, we need to reunite behind a new leader and we have to put the divisions of the past behind us.
"We have to draw a line under it and we have to form a credible opposition to take on Tony Abbott.
"It would take a minor miracle I think to get me back there."
Late last night, Senator Wong said she was shocked by the Labor Party's performance in the Senate.
"I haven't given up hope. It's certainly very disappointing and unexpected that we're in the position we're in, but I haven't given up hope," she said.
Political commentator Clem Macintyre says the result is likely to spark infighting behind closed doors.
"I think [it] will open up a number of wounds inside the Labor Party and there'll be a bit of point scoring and some scores to settle there," he said.
Professor Macintyre said the level of support for Senator Xenophon is an "unprecedented" result for an Independent.
"I can't think of any case in the country where an independent has got that level of support," he said.
"Brian Harradine was a successful senator in Tasmania for a long time but never received votes of 25 per cent."
Sarah Hanson-Young was widely tipped to lose her spot after Senator Xenophon preferenced the major parties ahead of her, a decision that prompted a five-week public spat between the pair.
Senator Hanson-Young believes she will retain her spot in Parliament.
"It's very much on a knife edge. I've always said that this race was going to be a tough one," she said.
"The Greens are in the race and we're going to have our fingers crossed and our toes crossed and hope that the numbers fall where they need to."