Tennis authorities have taken no action despite repeated warnings that a network of players on the professional circuit are suspected of match-fixing, an investigation by two media organisations has revealed.

Key points: 16 players lost games when suspicious bets were placed against them, the reports say

16 players lost games when suspicious bets were placed against them, the reports say Players targeted in hotel rooms and offered $73,100 or more per fix

Players targeted in hotel rooms and offered $73,100 or more per fix One player due to compete in Australian Open suspected of fixing his first sets

One player due to compete in Australian Open suspected of fixing his first sets Tennis authorities aware of match-fixing, but ATP president believes any activity on "incredibly small level"

BuzzFeed News and the BBC have revealed details of their investigation as the first grand slam tournament of the year, the Australian Open, is set to begin at Melbourne Park.

The findings of the joint investigation included:

A US Open champion and doubles winners at Wimbledon were among a core group of 16 players who had repeatedly been reported for losing games when highly suspicious bets have been placed against them;

A US Open champion and doubles winners at Wimbledon were among a core group of 16 players who had repeatedly been reported for losing games when highly suspicious bets have been placed against them; One top-50 ranked player competing in the Australian Open is suspected of repeatedly fixing his first set;

One top-50 ranked player competing in the Australian Open is suspected of repeatedly fixing his first set; Players were being targeted in hotel rooms at major tournaments and offered $US50,000 ($73,100) or more per fix by corrupt gamblers;

Players were being targeted in hotel rooms at major tournaments and offered $US50,000 ($73,100) or more per fix by corrupt gamblers; Gambling syndicates in Russia and Italy have made hundreds of thousands of dollars placing highly suspicious bets on scores of matches — including at Wimbledon and the French Open;

Gambling syndicates in Russia and Italy have made hundreds of thousands of dollars placing highly suspicious bets on scores of matches — including at Wimbledon and the French Open; The names of more than 70 players appear on nine leaked lists of suspected fixers who have been flagged to world tennis authorities over the past decade without being sanctioned.

ATP president Chris Kermode told a press conference in Melbourne that there was no truth to suggestions that tennis authorities were not taking match-fixing seriously or failing to investigate allegations.

"The Tennis Integrity Unit and the tennis authorities absolutely reject any suggestion that evidence of match fixing has been suppressed for they reason or isn't being thoroughly investigated," he said.

"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."

Kermode had earlier told the BBC that while match-fixing did occur in tennis, he believed it was at an "incredibly small level".

Report looked at analysis of betting on 26,000 tennis matches

Evidence uncovered by the joint investigation also included a bundle of leaked internal documents — the so-called Fixing Files — and analysis of betting on 26,000 tennis matches.

The leaked files reportedly contained evidence of suspected match-fixing by gambling syndicates based in Russia and Italy uncovered as a result of an investigation in 2008, but over which no action had been taken.

The gambling analysis found 15 players whose matches regularly had heavily one-sided betting that substantially shifted the odds — seen as an identifier of possible match-fixing.

Four players showed particularly unusual patterns — they had lost nearly all of the matches where gamblers had betted heavily on one side.

Given the initial odds, the chances that the players would perform that badly were less than one in 1,000.

The 2008 investigation was triggered by a notorious match in Poland in August 2007 between Russia's Nikolay Davydenko and Argentine player Martin Vassallo Arguello, which attracted millions of dollars' worth of highly suspicious bets from Russian-based accounts.

The ATP found no evidence of rule-breaking by either player.

However, the leaked files reportedly showed that Vassallo Arguello exchanged 82 text messages with the suspected ringleader of an Italian gambling syndicate.

Italian and Russian gambling syndicates and another in Sicily were found to have placed suspicious bets on 72 matches involving 28 players that the investigators flagged to the authorities.

Match-fixing easy to do, says former player Koellerer

In 2011, Austrian player Daniel Koellerer was banned for life for match-fixing and fined $US100,000 ($146,200) by the Tennis Integrity Unit, but the court overturned the fine as he had not benefited financially from the charges for which he had been found liable.

Koellerer denies the allegations, but told the BBC he had been approached to fix matches on a number of occasions.

"In Chennai, they offered me $US50,000 ($73,100) to lose to Davydenko in the first round and in Paris, they offered me double money to lose in straight sets and also a bigger amount than $50,000 against Tipsarevic in Moscow," he said. "I didn't even think about fixing the match and taking the money."

However Koellerer said it would be easy for a professional player to fix a match without spectators being able to tell.

"As a tennis player, you cannot believe how easy it is to play the ball next to the line, but not in the field, out," he said.

"No one from 10,000 people watching the match will realise if this match is fixed or not.

"So you just play two sets, lose 6-4, 6-4, get one break, serve a double fault in the game where you get the break and the thing is done."

Suspected players appearing on lists 'time and time again'

Sorry, this video has expired Significant evidence of match fixing among tennis top 50: Buzzfeed

BuzzFeed UK investigations editor Heidi Blake told ABC News 24 that nine lists of players suspected of involvement in match-fixing had been sent to the Tennis Integrity Unit at Wimbledon since 2008.

"We can see the same 16 names appearing time and time again on those lists," Blake said.

"A core group of players, all of whom have ranked in the top 50, and half of whom are about to begin playing at the Australian Open on Monday.

"We can see that these guys just coming up again and again. Many of them were flagged back in 2008 by the investigators hired by the association of tennis professionals and yet they're all still playing."

Tennis Integrity Unit set up after 2008 probe

The Tennis Integrity Unit (TIU), set up in the wake of the 2008 investigation, has disciplined 13 low-ranking male players for fixing since its inception and banned five for life.

The leaked files revealed investigators implicated 28 players in suspected fixing and urged that they face a full disciplinary investigation.

But TIU head Nigel Willerton said authorities had drawn a line under the evidence uncovered, because lawyers had advised that a new integrity code introduced in the wake of the 2008 investigation could not be enforced retrospectively.

"As a result, no new investigations into any of the players who were mentioned in the 2008 report were opened," Willerton said.

Willerton told Buzzfeed the sport took "a zero-tolerance approach to all aspects of betting-related corruption" and "all credible information received by the TIU is analysed, assessed and investigated by highly experienced former law-enforcement investigators".

Ben Gunn, a former police chief who led the review that recommended the formation of the TIU after 2008 said world tennis was failing to confront the issue of match-fixing.

He said authorities had missed "a perfect opportunity" to clean up the sport.

"What they did is a plastic solution which was not effective then and it's not effective now."