Mum warns other cyclists about being out at night after her son River Caldwell died north of Hokitika

River Caldwell, 16, was struck by vehicles twice on SH6, north of Hokitika in the early hours of August 24. Photo / Supplied

The mother of a teen who was killed cycling at night heard about the accident on the news but didn't know it was her son until later.

River Caldwell, 16, was struck by vehicles twice on SH6, north of Hokitika in the early hours of August 24.

An SUV traveling the same direction as the boy hit him from behind. River was tossed onto the other side of the highway where he was hit by a large truck and trailer unit.

His mum Sheree Caldwell told Fairfax she wants her son's tragedy to be a warning to others who cycle at night.

River wore a headlamp, but no helmet or high-vis when he was hit.

Caldwell told Fairfax that her son was biking home from his girlfriend's house when he was killed. The last time she saw him was around 9pm the night before when he told her he was going to have an early night.

The next morning she heard about the accident on the news, Fairfax reported. When she saw her son and his brother's bike was missing she started to panic.

"I knew something wasn't right. I rang his girlfriend's mum. I told her there'd been a terrible accident and she asked her daughter. She burst into tears and said had left just after 6am. I knew right then and there."

She rang the hospital and police, but could not get any information.

"I was frantic. Thinking about him lying on the road."

Later that morning, her husband, Brett, came home and told her River had died.

"I want teenagers to listen to their parents and think before they make bad decisions. They think they are invincible," she said.

She had told him to stop cycling at night as it's dangerous.

"Everyone tried to talk him out of it. I just knew he'd have an accident and I warned him about it," Caldwell said in her first interview since his death.

"I keep thinking it over. What could I have done? You couldn't stop him. It's been the worst nightmare that anyone could ever have. I just wish it wasn't him."