Emergency services were called to the collision just south of the Mount Cook turn off at 6.15am on Wednesday.

A 62-year-old English man is in a stable condition after a collision near Twizel in which his cycling partner was killed.

Emergency services were called to State Highway 8 near the Mt Cook turn off at 6.30am after the two cyclists were hit by a truck.

Westpac Rescue Helicopter intensive care paramedic Mike McLintock said a 62-year-old English man was initially assessed as being in a serious condition but had been reassessed as stable once they arrived at Christchurch Hospital.

SUPPLIED/WESTPAC RESCUE HELICOPTER One cyclist was killed and another injured after colliding with a truck near Twizel on Wednesday morning.

A St John spokesman confirmed one person had died at the scene following the crash just south of the Mt Cook turn off at 6.15am on Wednesday.

Senior Constable Les Andrew, of Twizel police, said the serious crash unit was investigating.

The truck involved in the collision was operated by Metro Performance Glass. Chief executive Nigel Rigby confirmed the truck was transporting glass from Christchurch to Central Otago.

Rigby said the incident was "very regrettable".

"It is still under police investigation, so we don't know a great amount," he said. The truck left the company's Christchurch factory at 3am.

"Our driver is obviously very shaken and shocked by what has happened."

He said the company operated around 200 trucks across the country and all were equipped with satellite tracking, "so we know where it was and its speeds".

Andrew said the truck appeared to have been travelling south when the crash happened on a "completely straight stretch of road".

The weather on Wednesday morning had been foggy in Twizel. Conditions at the scene had been clear, although it would have been dark when the crash happened.

It was "too early to say" what had caused the crash, Andrew said.

SH8 reopened about 1.30pm.