SYDNEY (Reuters) - Voters began casting ballots in a Sydney by-election on Saturday that could determine the future of Australian Prime Minister Malcolm Turnbull, who is hoping to regain his parliamentary majority and safeguard his leadership.
The election campaign in the blue-ribbon Sydney seat of Bennelong has been bitterly fought between the center-right government's candidate, former tennis star John Alexander, and the Labor opposition's Kristina Keneally, a high-profile former premier of New South Wales, Australia's most populous state.
The outcome of the election could have serious repercussion's for Turnbull's conservative coalition. If Alexander loses, the government will again be forced to govern in minority and rely on the support of independent lawmakers.
John Warhurst, a professor of political science at the Australian National University in Canberra, said Turnbull's position would be untenable should the government lose the by-election.
"Everything would be on the table, including Malcolm Turnbull's leadership," Warhurst said.
Alexander is re-contesting the seat after he stepped down in early November when he was swept up in a citizenship crisis that has so far seen 10 lawmakers leave parliament, either forced out by court rulings or by their own choice.
He left parliament because he believed he might hold dual British citizenship, which he has since rescinded. Australia's constitution bars foreign nationals from sitting in parliament to prevent split allegiances.
Turnbull's coalition has been forced to govern in minority since October, when the citizenship crisis cost him several cabinet members and wiped out his razor-thin majority. Among those forced out was Turnbull's deputy, Barnaby Joyce, who has since won back his seat.
"People will be casting a judgment on the government, which I lead, of course," Turnbull told Melbourne radio station 3AW.
Alexander is also favored to win back his seat, but the comfortable margin of almost 20 percentage points that he won by in 2016 is expected to shrink significantly after a robust campaign by Keneally and Labor, who have urged voters to use the election to punish the government.
The race tightened in recent days amid a diplomatic spat between Australia and China, sparked when Turnbull accused Beijing of improper interference in Canberra.
One in five Bennelong voters has Chinese heritage and Turnbull's Liberal Party fears a backlash in a potentially tight race.
Turnbull, who has lagged in opinion polls all year, and his minority government have already been forced to accept a widespread banking inquiry after independent members in parliament flexed their new-found power.
Results of the by-election may not be announced until Sunday, due to the high number of postal votes made before the election and which are always counted last.
(Reporting by Colin Packham in SYDNEY and Alana Schetzer; Editing by Paul Tait)