Fellow racer and pundit Andrew Fitzgerald tweeted that the May family have confirmed he's in a stable condition and they aren't yet sure what caused the medical event or what it was.
May, who was driving top-class pacer A G's White Socks in the Central Otago Trotting Cup, collapsed before being dislodged from his race sulky, and lay prone on the track.
The quick actions of his fellow drivers and trainers are believed to have been crucial in keeping May alive.
Two drivers were quickly at his side to perform CPR which revived him.
A specialist cardiac nurse and an off-duty paramedic were quickly on the scene and played a vital part in tending to May. Racegoers and others also assisted.
May was subsequently taken by helicopter to Dunedin Hospital about 5.30pm.
The crowd of about 5000 was left in shock by the incident. Many stood and cheered as the helicopter carrying May left the racecourse.
Afterwards, many people who went to cash in their tickets stayed to donate the money to St John's Ambulance or May's family.
Harness Racing New Zealand chairman Ken Spicer was at the race meeting.
"The quick actions of the horse people, racegoers and race-day staff may have saved Ricky's life,'' he said.
"It is important that everyone in the harness racing family gets behind Ricky and his family."
May was driving A G's White Socks for Canterbury trainers Greg and Nina Hope.
Greg Hope described May as a highly respected and popular driver.
"No-one has got a bad word to say about Ricky.
"He is a great friend of our family.
"Everybody in the industry is behind him and his family and all we can hope for is the best for him."
Hope said May appeared to be fit and healthy before the race.
"Before he got in the cart he was 100 per cent right ā at no stage did he look crook."
May lives at a rural property near Methven with his wife, Judy. The couple have three children, Tim, Phil and Kate.
The Omakau races were called off at 5.10pm.
Racing Integrity Unit official Nigel McIntyre said May's colleagues unanimously agreed that the meeting should not continue.
"We met with all of the drivers and the Harness Racing New Zealand board members that were here and it was a unanimous decision that the meeting should not continue."
May is one of the most popular and successful harness racing drivers in New Zealand.
He has won 2948 races in New Zealand during a career of more than 40 years. That tally is the third-highest in the history of the sport in this country.
May has the greatest record of any driver in New Zealand's biggest harness race, the New Zealand Cup at Addington. He has won the race seven times.
