Tennis authorities vigorously denied suppressing match-fixing claims on Monday after a bombshell report alleging widespread corruption cast a shadow over the start of the Australian Open.

The BBC and BuzzFeed reported that a "core group" of 16 players who reached the top 50 in the past decade, including Grand Slam title-winners, had repeatedly caused suspicion but never faced action.

The claims, citing a leaked cache of secret files, broke as the year's first Grand Slam got underway in Melbourne, and prompted a swift response from tennis officials.

As speculation swirled over the identities of the suspected players -- eight of whom are reportedly in Melbourne -- world number one Novak Djokovic said he was once approached to fix a match.

The men's tour and the sport's anti-corruption body, the Tennis Integrity Unit, as well as Tennis Australia firmly rejected suggestions that any evidence was deliberately suppressed.

"The Tennis Integrity Unit and the tennis authorities absolutely reject any suggestion that evidence of match-fixing has been suppressed for any reason or isn't being thoroughly investigated," men's tour chief Chris Kermode told reporters.

"And while the BBC and BuzzFeed reports mainly refer to events from about 10 years ago, we will investigate any new information, and we always do."

Tennis Australia chief executive and Australian Open tournament director Craig Tiley hit out at the timing of the report, and said the season's first Grand Slam was known for its integrity.

"In conjunction with world tennis we have developed leading anti-doping, disciplinary, anti-corruption and security policies," Tiley said in a statement.

Murky world

The leaked files include details of an investigation into a 2007 match between Nikolay Davydenko and Martin Vassallo Arguello, which found insufficient evidence of corrupt practice.

The report said the probe uncovered syndicates in Russia and Italy making hundreds of thousands of dollars betting on matches investigators thought to be fixed.

The key group of 16 suspect players had not been targeted in any crackdown, it said, questioning the effectiveness of the Tennis Integrity Unit (TIU).

But Kermode said the TIU had won 18 convictions including six life bans since it was set up in 2008, adding it "has to find evidence as opposed to information, suspicion, or hearsay".

BuzzFeed said players were targeted in hotel rooms at major tournaments and offered $50,000 or more to fix matches for the betting syndicates.

Other allegations included that a confidential report in 2008 recommended investigations into 28 players but the findings were not followed up, apparently on legal advice.

The report also said the European Sports Security Association, which monitors betting for bookmakers, flagged up more than 50 suspicious matches to the TIU last year.

Djokovic played down the report's significance but he also said he was targeted in 2007 to throw a first-round match at St Petersburg.

"I was not approached directly. I was approached through people that were working with me at that time," said the defending Australian Open champion, after beating Chung Hyeon in the first round.

"Of course, we threw it away, right away. It didn't even get to me, the guy that was trying to talk to me, didn't even get to me directly. There was nothing out of it."

Djokovic was reportedly offered $200,000 to throw the match, in an incident which gives an insight into the murky world of match-fixing -- which the Serb called "a crime in sport".

Other players seemed unaware of any problems with corruption, with both Serena Williams and Japan's Kei Nishikori saying they hadn't noticed anything untoward.

"When I'm playing, I can only answer for me, I play very hard, and every player I play seems to play hard," said Williams after beating Camila Giorgi in the first round.

"I think that... as an athlete, I do everything I can to be not only great, but, you know, historic. If that's (match-fixing) going on, I don't know about it."