At 9.45pm with 18 per cent of the votes counted, the Coalition had secured 11 seats and appeared set to win another four. Labor had also won 11 Senate spots while the Greens appeared on track for four seats.

The final Senate results are not expected to be known for several weeks.

Forty seats are being contested in this federal election - six in each state and two in each territory. Across Australia, 458 candidates vied for an upper house spot.

Federal elections are won and lost in the House of Representatives, but the make-up of the Senate is critical to whether the government of the day can implement its full agenda.

Neither Labor nor the Coalition is likely to control the Senate, meaning they will have to negotiate with the Greens, micro parties or independents to pass legislation.

New Senate voting rules introduced before the 2016 election prevented obscure micro-candidate parties with very low primary votes from swapping preferences to wrangle an upper house seat.

That means the next parliament is unlikely to see a repeat of what Tony Abbott described as the ''feral'' Senate elected in 2013, including Ricky Muir of the Motoring Enthusiast Party, who attracted a mere 479 primary votes.

However, candidates from smaller parties remain a good chance to nab a handful of Senate spots. Contenders include controversial mining magnate Clive Palmer, of the United Australia Party, who has spent $60 million on political advertising in his bid for a Senate comeback. His chances have been helped by a preference deal with the Coalition.

Mr Palmer is considered the main threat in Queensland to Pauline Hanson's One Nation candidate, Malcolm Roberts. The two are also up against far-right senator Fraser Anning, who is predicted to lose his Senate spot.

On the progressive side of politics, the Greens are defending six of their nine Senate seats at this election - one in every state. The party is in for a tough contest in NSW, Queensland and South Australia, and appears unlikely to hold the balance of power in the next Senate.