Riversdale father-of-two Lindsay Roy died during the 140km Milton Lake to Sea trail ride at the weekend.
He was one of 870 people taking part in the 18th annual fundraiser for Tokomairiro High School PTA.
The 52-year-old came off his bike in sunny, dry conditions on one of the event’s many forestry sections.
A Gore rider, who did not want to be named, said he and friends came over the brow of a gravelled forestry road about noon, to discover a boy of about 11 lying prone in the road, surrounded by other riders who had stopped to help.
Mr Roy and his motorcycle were not immediately apparent, he said.
"About a dozen riders were stopped in the middle of a wide, gravel straight, with a section of cleared forestry to the right down a 6m bank.
"We ran up to help the kid, and someone pointed out a second bike down the bank about 40m away.
"The kid had sat up by now, so we headed over to the second rider, who was about halfway down the bank and in a bad way.
"Within about 30 seconds, a first-aider turned up and took control, so we did crowd control for a bit, before eventually moving on."
He said those he spoke to at the scene said the adult rider and junior had collided.
The area was one of several where the different trails in the event crossed.
"We’re all pretty shocked. It’s just a terrible thing to have happened for everyone concerned."
He believed blame should not be placed on event organisers, who had taken "every measure" to ensure rider safety.
"It’s one of the best organised and run events out there.
"Everyone was well briefed, and it’s always emphasised it’s not a race, but a fun ride."
Another fundraising trail ride is scheduled to take place in nearby Kaitangata, on November 15.
Kai Bush Bash organiser Dallas Storer, who suffered a serious accident during a Catlins trail ride two years ago, said he felt for the organisers of the Milton event, and for Mr Roy’s family.
"No-one ever wants this to happen, but having run our event for several years and experienced a crash in person, I know how quickly things can turn to custard."
Mr Storer hoped there would not be a "knee-jerk" regulatory response from authorities.
"Organised events like these allow people to ride out legally and without annoying others, and organisers really run them for the love of it.
"We’ve had a few people asking about the Bush Bash, but we’re planning to go ahead at this stage. Everyone’s been very supportive."
WorkSafe said it had been notified of the incident.
"We are making initial inquiries to establish what our next steps might be. This includes whether or not an investigation will be launched," a spokeswoman said.
Police were continuing their inquiries yesterday.
