Winston Peters says the alleged offenders should be treated as innocent until proven guilty.

A 17-month investigation into alleged harness race fixing, corruption and drugs in the sport is unprecedented in New Zealand, police say.

Teams of police began Tuesday with raids on properties in Canterbury, Invercargill and Manawatū. No arrests were made, but police said charges were expected.

Well-known racing figures interviewed included Natalie Rasmussen, John Dunn, Blair Orange, Nigel McGrath and Andrew Stuart.

Dean Kozanic The home of Christchurch car industry king pin, racehorse owner and major punter Graham Beirne was raided by police but Beirne says the allegations are "nonsense".

Harness racing turns over about $220 million a year in betting and receives about $40m from the Racing Board. About 11,000 people are believed to own horses trained for harness racing, industry reports say.

READ MORE: Police, racing integrity unit investigate race fixing allegations

Racing Minister Winston Peters said the raids showed the industry's integrity unit was working as intended.

STACY SQUIRES/STUFF Police a property in Woodend Beach, where Robert Dunn's Canterbury stable operates. His training operation is overseen by his eldest son and stable foreman, John Dunn.

"If anybody thinks, in that industry, that they're above the law or above the requirements of integrity they couldn't be further from wrong."

Peters stressed only "one small group" was alleged to have "fouled the rest of the industry's good reputation".

"I would like to hear the evidence first because we can't rush to judgment. They have got the right to be regarded as innocent until being proven guilty and I cannot, as minister, contaminate that objective."

STUFF In September 2018 police raided harness racing stables across the country amid allegations of race fixing and corruption as part of Operation Inca. Stuff understands much of the evidence in relation to the earlier drug charges against Matt Anderson was gathered during Operation Inca. (Video first published in September 2018)

Detective Superintendent Tim Anderson said would not comment on the allegations surrounding drug use but said it "was possible" drug charges could be laid.

It was not yet known how much money could have been tied up in fixed races, he said.

RACING FIGURES RAIDED

DAVID WALKER/STUFF Detective Superintendent Tim Anderson says "a lot" of arrests are expected in relation to allegations of race fixing.

Christchurch car industry king pin, racehorse owner and major punter Graham Beirne, speaking to Stuff from Bali where he is on holiday, said he had heard about the raids on Canterbury trainers and knew police wanted to interview him.

"If they are talking race fixing, it's nonsense. It doesn't happen, so we'll see what they come up with but they are obviously taking it seriously because they have raided stables all over the place."

Four police cars and 12 police officers had come to his Fendalton house to execute a search warrant on Tuesday morning and apparently seized computers and devices, he said.

DAVID WALKER/Stuff National Manager Criminal Investigations Detective Superintendent Tim Anderson briefed media in Christchurch on raids at properties across the country in relation to match fixing in harness racing.

"But I haven't made any money in the last two years. The TAB records will show that."

Race fixing may have occurred in the distant past but checks and balances in the current system made it too difficult, he said.

He had about 30 horses that were trained by a number of trainers.

STUFF John Dunn has been interviewed by police in relation to the investigation.

"I don't need to race fix ... I've got the pension now."

'BIG GUYS' THE FIRST SUSPECTS

Champion trainer Mark Purdon said police arrived with a warrant to search his home and business, All Star Stables, on Tuesday morning.

Police have talked to trainer-driver Nigel McGrath.

Police were not interested in him but his businesss partner, Natalie Rasmussen, was still being questioned by police at 4pm, he said.

"I wouldn't have thought she would have anything to worry about," Purdon said.

"I certainly know as far as race fixing goes and drugs, they will draw a blank with us ... we pretty well keep to ourselves."

Race Images Police have also talked to Blair Orange.

He was surprised by the allegations against other trainers but said "the big guys" were often the first suspects.

"They always pick on the people that are having the success."

New Zealand Racing Board head of communications Kate Richards said TAB betting had not been suspended.

DAVID WALKER/STUFF Police were at Mark Purdon and Natalie Rasmussen's All Stars Harness Racing property at Rolleston, Canterbury, on Tuesday. Purdon says police did not question him.

The board was actively monitoring the situation and would review the situation depending on the outcome of Tuesday's events, she said.

Harness racing participants race for more than $28m in prize money annually. More than 250 drivers participate in about 265 race meetings around the country each year. Just over 30 per cent of those meetings are held in the Canterbury region.

SYSTEM 'WORKING'

JOSEPH JOHNSON/STUFF Mark Purdon and Natalie Rasmussen at Addington Cup Week in Christchurch in 2016.

In a written statement, New Zealand Racing Board chairwoman Glenda Hughes said the investigation "while disappointing, shows the racing integrity system is working".

The board's chief executive, John Allen, said he was confident alleged breaches would be "investigated and prosecuted appropriately".

"Those involved in the industry and the Kiwi punters who support it must have confidence in the integrity of the sport."

RICKY WILSON/STUFF Police have raided harness racing stables around New Zealand. (File photo)

Harness Racing New Zealand chief executive Edward Rennell confirmed he was aware a police operation was under way but had no further details.