Canterbury Westpac Rescue Helicopter intensive care paramedic Mike McLintock said his crew flew two patients - a 15-year-old girl with pelvic injuries and a 56-year-old man with chest injuries - to Christchurch Hospital.
The pair were assessed as being in a moderate to serious condition.
"Obviously with a pelvic injury you have to be a bit careful," he said.
Witnesses told him the cyclists had clipped each others' wheels on the final stretch and others behind them had toppled over them.
Canterbury rural area police commander Inspector Peter Cooper told Stuff two competitors had been vying for first place when they collided and "collected each other" near the finish line.
"It often happens in cycle races; they would have been sprinting like the clappers so when they went down, the others followed," he said.
The Canterbury District Health Board said staff saw seven injured riders, and three were admitted to hospital.
Anderson was about 100m behind the crash. It wasn't clear what caused it, but he said no motor vehicles were involved.
He said that of the 40 or so riders in the race, about 30 were in the bunch and he understood nine were attended to by St John ambulance staff.
Two riders were flown to hospital by rescue helicopter.
"There's a lot of grazed people and gravel rash."
Spectator Shane Epiha, who looks after the club's juniors aged 11 to 14, was standing 200-300m from the crash.
"I'm not sure exactly what happened; there's been a touch of wheels or something along those lines and then just everyone went down - it was terrible to see."
"One of the junior's dads is involved and he had a broken collarbone, so he was quite groggy when we got there, but there was already two people helping him," Epiha said.
"There was bikes sort of strewn all over the place. I believe one of the bikes was broken in half."
Leeston Fire Brigade station officer Roger Sheat described the scene as being chaotic.
Speaking to Stuff, he said "even the riders didn't seem to know what had happened".
"There were a whole group of riders all over the road and something's happened and they've gone down and all tumbled after each other."
He told Stuff there had been fears that some of those involved in the crash had internal injuries.
"Obviously when you fall off a bike at those kind of speeds, there can be unknown injuries," Sheat said.
