Emergency services were called to parkland off Ashmont Avenue in Ashmont, just before 12.30am after reports a trail bike had crashed.

Riverina Police District officers and NSW Ambulance paramedics attended the scene.

A 14-year-old boy from Ashmont who was on the bike was taken to Wagga Base Hospital in a critical condition.

He is now in a stable condition and will be airlifted to Sydney Children's Hospital today.

A 23-year-old man who was also on the bike was injured and taken to Wagga Base Hospital in a stable condition.

The unregistered trail bike was being ridden on a dirt track when it crashed into a culvert and threw the boy and the man to the ground.

The man then alerted emergency services to the incident.

Initial information provided by police said the 14-year-old was the rider and the 23-year-old was his passenger.

However, Riverina police detective chief inspector Winston Woodward would not confirm who was riding the bike.

Inspector Woodward said police believed the two males were acquaintances, but the full details of their relationship would not be known until an investigation was completed.

Inspector Woodward said it was unknown what speed the trail bike was travelling at.

He said the bike was not stolen, and police had spoken to its owner.

"It just appears they were out on the bike at night and without the appropriate safety equipment," he said.

Police believe neither of the males were wearing helmets.

Inspector Woodward said this significantly contributed to the boy's head injuries.

"It's a timely reminder that young people have for years and will into the future ride unregistered trail bikes," he said.

"I don't like giving safety messages at sad times such as these ... however if you do ride trail bikes please use the appropriate safety equipment and always wear a helmet to protect your head."

Riding an unregistered trail bike is an offence, however Inspector Woodward said police would not yet discuss any charges due to the serious nature of the boy's injuries.

"I think the head injuries he's sustained it will take him a while to get over. And it may see the fact that police can't talk to him for some time to come," he said.

A crime scene has been established, and detectives are continuing to investigate the circumstances surrounding the crash.

Anyone with information about the incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence. The public is reminded not to report crime via NSW Police social media pages.