The cliff collapsed near Northside, Birsay, in the north west of mainland Orkney, with dramatic photos showing the impact of the rock fall.
The affected area runs close to St Magnus Way, a 58-mile pilgrimage route across the island, with the area also popular among those hoping to catch site of nesting puffins.
The public have been warned to stay back from the cliff edge and not to venture to the area to see the aftermath of the cliff collapse. A brightly coloured algae plume has now formed at the site.
A spokeswoman for Orkney Islands Council said the collapse was unexpected.
It is thought the cliff fall was caused by Atlantic waves weakening the base of the cliff.
A statement from the local authority said: “Cliff falls are unpredictable and this one was not, to our knowledge at this stage, one that was expected.
"We’d just stress the often rehearsed advice to stay well back from cliff edges when enjoying the coast. We’d also plead with locals and visitors not attempt to get close to this latest fall for a better look – it is simply not worth the risk.”
Orkney resident Michael Budge photographed the cliff fall and said its impact had been “striking”.
He said: “Right above it is St Magnus Way and it can be quite a dangerous stretch.”
Mr Budge said the cliff fall was in the same location as the October 1924 shipwreck of the Hull-based fishing trawler Hessonite, which became trapped on the rocks in a storm with ten men saved from the vessel.
A statement from St Magnus Way said the stricken cliff was “fortunately not too close” to the walking path.
It added the cliff fall was “was a good reminder that everyone walking the St Magnus Way needs to be very wary when close to cliff edges”, adding: “They are not stable and may give way at any time.”
A spokeswoman for NatureScot, the government agency that protects the natural environment, said it was aware of the incident.
She said: “ As to possible reasons why this might have happened, wave action can erode the material at the base of a cliff, resulting in the cliff above becoming unstable.
"Depending on their geology, this can lead to a cliff collapse. The Birsay cliff is exposed to strong westerly seas, so this may have been a factor in the collapse.”
The St Magnus Way opened at Easter 2017 to mark the 900th anniversary of the death of St Magnus, Orkney’s patron saint.
It opened to revive the ancient practice of pilgrimage, which was cast aside as superstitious during the Reformation.
The route was also set up to emulate the popularity of similar routes across Europe, such as the Camino de Santiago in Spain.
The walk is broken into six stages, with the first connecting Evie to Birsay to reflect the route of Magnus's body as it returned from Egilsay where he was murdered on the instructions of his cousin, Hakon, probably in 1117.
The walk ends at St Magnus Cathedral in Kirkwall, which was built by his nephew St Rognvald around 20 years after his death.