Betting markets on five races at New Zealand's richest harness race meeting have been suspended amid fears some horses from the All Stars stable could have been contaminated with a prohibited substance.

Natalie Rasmussen, who operates the stable with Mark Purdon, told the NZ Racing Integrity Unit of concerns regarding possible human-to-horse contamination from one or two of the people accompanying the horses from the South Island to Cambridge.

"We have advised the appropriate bodies of the possibility and all our horses will be urine tested on Thursday. We are not expecting any adverse outcome from those but we just want to be sure and keep everything out in the open" Rasmussen said on the stable's website.

"The incident goes back several days but we want to be absolutely sure there is no possibility of our horses being compromised as a result.

"We are not expecting withdrawals from any of the races. We are just taking every precaution."

The NZ RIU says results of the tests will not be known until Friday, the day before the meeting.

The horses affected are Princess Tiffany, Winterfell, Sicario, Kayla Marie, Funatthebeach, Stress Factor, Cheerful, War Dan Delight and Bubbled Up.

Dibaba, from Terry and Glenys Chmiel's stable, will also be tested because she travelled with the nine Purdon-Rasmussen trained horses.