A man's death after he stumbled and fell off a cliff while having his photo taken at a Canterbury gorge has been ruled an accident.

Darryl Richard Kitto, 47, who was intellectually disabled and had two caregivers, fell down the Rakaia Gorge cliff on April 17, 2016.

Coroner Sue Johnson released her findings into Mr Kitto's death on Friday, ruling it was an accidental but preventable death.

Mr Kitto had been standing about two metres from the cliff's edge when his caregiver stepped back to take his photo.

In these few seconds, Mr Kitto, who had stepped down to a lower mound to fit in the photo, stumbled and fell around 30-40m over the cliff.

Ms Johnson said there was no evidence anyone knew how dangerous the steep slope was.

The NZ Transport Agency (NZTA) will install a 1.2m-high steel fence around the perimeter of the car park in the coming weeks.

It will also erect signs indicating the carpark is a formal rest stop.

Ms Johnson has supported NZTA's approach.

- NZN