A champion Australian harness racing driver is one of four industry insiders implicated in an alleged race fixing operation identified by Victoria's elite anti-sports corruption police taskforce.

Fairfax Media can reveal that detectives arrested the four harness racing industry participants on Sunday early evening, after the Breeders Crown at TAB Park in Melton. The event is one of the biggest harness meets in Australia.

It is the second time in as many years Victoria Police has uncovered alleged harness race fixing in an industry that generates tens of millions of dollars in gaming revenue for the state government.

The race fixing allegations will be keenly watched by Victoria's thoroughbred racing administrators on the eve of the Spring Carnival.

One of the suspects in the police investigation that prompted Sunday's raids - champion driver Nathan Jack - has previously been suspected of leaking inside information to punters to increase their betting odds. Analysis of Mr Jack's TAB accounts has previously uncovered an allegedly suspicious transaction.

Police were still questioning Jack and the other arrested industry insiders on Sunday night.

The police operation was triggered by sensitive betting activity involving a race in June last year, which stewards and police suspect may have been fixed.

The inquiry has been examining whether a small number of harness racing industry identities have engaged in 'cheating in sport' offences, including manipulating a race to effect a betting outcome. Those found to have breached the laws can face serious penalties, including jail terms and large fines.

Harness racing is regarded as the poor cousin of thoroughbred racing, with the smaller prize pools and a racing format that may make it easier for cheats to target. But certain figures known to police float between harness and thoroughbred racing.

It is understood harness racing investigators have worked with police on the inquiry that prompted the arrests on Sunday. Harness racing has reformed its anti-corruption unit as part of a push by racing minister Martin Pakula to improve integrity measures across all three racing codes.

The inquiry was led by Victoria Police's Sports Integrity Unit, which was set up by chief commissioner Graham Ashton several years ago amid warnings that the huge growth in online and sports betting, including in underground markets, posed a major risk to Australian sport.

It is the only full time anti-sports corruption police taskforce in the nation.

The unit has led several major probes since its inception, including an operation that uncovered match fixing involving a semi-professional Victorian soccer team, the Southern Stars, and an inquiry into suspected corruption on the professional tennis circuit.

In 2015, detectives from the unit arrested and charged two leading harness racing figures, father and son team Shayne and Greg Cramp. The pair later avoided jail terms when they pleaded guilty to race fixing offences and received 12-year bans from the sport.

The Cramps were superstars of the sport in Victoria, although they were also suspected by many industry insiders to be corrupt. After they were arrested and suspended, there was an increase in betting on races in which the Cramps' usually competed. The increase in betting suggested punters had more confidence in the sport with the pair removed.

Nathan Jack's alleged misconduct has been previously analysed by detectives. Fairfax Media has uncovered information suggesting Mr Jack may have previously passed racing tips to big Victorian gamblers, including a betting syndicate led by underworld identity Paul Sequenzia.

Sequenzia is well known to thoroughbred, harness racing and AFL integrity investigators as he has close ties to insiders in all three codes and is suspected of using inside information to punt.  There is no suggestion Sequenzia has any connection to the arrests on Sunday.

Victoria's Racing Integrity Commissioner, Sal Perna, said the arrests underscored how Victoria's approach to detecting alleged sporting corruption is working.

"There will be instances from time to time that cause sporting controlling bodies to raise suspicions with the police, who then conduct separate investigations. This is a great example of how the sports integrity system should work."