"As it turns out, they met by crashing into each other," he said.
The site had been mostly cleared by the time police arrived but an officer had spoken to the teenagers in hospital, Mr Matheson said.
Police are investigating the cause of the crash.
Castlepoint-based rural fire-fighter Anders Crofoot said paramedics and a Life Flight air ambulance crew were assisting the youngsters when firefighters arrived. Members of the public had also stopped to assist.
"One of the guys said his side was really hurting, so the paramedics were a bit concerned about internal injuries," Mr Crofoot said.
"I think he turned out okay, though - the experts did a great job."
Mr Matheson said it was one of two bike-related incidents Masterton Police had attended over the holiday weekend - with a man crashing his motorcycle on Nursery Rd at midday yesterday. The man "came off his motorbike" after losing control turning a corner, most likely due to wet road conditions, and was taken to Wairarapa Hospital with a broken collarbone.
Mr Matheson said no other vehicles were involved, and neither speed nor alcohol had played a part.