SYDNEY • Australia's election campaign was hijacked yesterday by police raids on the Labor opposition over a suspected leak of documents citing cost blowouts in a multibillion-dollar broadband upgrade, sparking concerns about abuse of power.

Labor questioned the timing of the raids and whether the government had put pressure on police, while Prime Minister Malcolm Turnbull and the head of the Australian Federal Police (AFP) rejected any suggestion of political interference.

The controversy capped the second week of campaigning ahead of a national election set for July 2, in which polls indicate a tightly contested race between Labor and Mr Turnbull's Liberal-National coalition government.

The unprecedented timing of the raids, which carried on until the early hours of yesterday morning, also led to concerns that it could have a negative impact on whistle-blowers.

"This is about the right for the public to know the truth," said Labor leader Bill Shorten.

"Mr Turnbull is going to extraordinary long lengths to stop Australians finding out the truth about the cost of the NBN (National Broadband Network). He is going after whistle-blowers and he is smearing his political opponents.

"The public have a right to know the truth and whistle-blowers have a right to protection."

Mr Turnbull said he had no prior notice of the raids and chastised Labor for questioning the integrity of the police.

"The first I heard of the AFP investigation was yesterday when I was advised by the Justice Minister shortly after he'd been advised by the Commissioner," he told reporters.

Asked if he or any of his staff had ever leaked confidential documents during his political career, Mr Turnbull said he was not going to get into a "fishing expedition".

Mr Turnbull was communications minister for more than two years before deposing Mr Tony Abbott in a party coup last year.

The NBN aims to connect 93 per cent of Australian homes and workplaces with optical fibre, providing broadband services in urban and regional areas. It was created in 2009 by the Australian government and is expected to be ready by 2020.

The AFP said in a statement it had informed both the government and opposition before conducting the raids, as was standard procedure. AFP Commissioner Andrew Colvin told reporters: "(With) regard to government and political influence that has been commented on this morning, there has been no influence, no influence on the AFP in the conduct of this investigation."

University of Sydney emeritus professor of political science and media Rodney Tiffen said the raids, coming as they did in the midst of a federal election campaign, were "unprecedented" and it was unclear how the situation would play out.

"I've never known anything at all like it in an election campaign," he told Reuters. "I think that's really the key question, whether it was politically motivated in some sense."

REUTERS