New Zealand harness racing driver Ricky May is in a stable condition after collapsing in the sulky while leading a race at Omakau.

A Dunedin Hospital spokesperson told Radio New Zealand on Friday, May was now in a serious but stable condition in the intensive care unit.

May suffered a medical episode on Thursday which at the time was thought to be a heart attack but that has not been confirmed.

May was stabilised on the track and flown to Dunedin Hospital by air ambulance after he first fell back into the sulky and then fell to the ground.

The meeting was abandoned after consultation with drivers and trainers.

May is one of New Zealand's most successful and experienced harness racing drivers, winning almost 3000 races in a career spanning more than 40 years.