Tonnes of rock and sand have fallen from a cliff where a housing development is planned.
Police said they were called by the coastguard to a "significant cliff fall" at Whipsiderry, near Newquay, on the afternoon of Wednesday 29 November.
Officers added nobody was reported injured.
Earlier this year, preliminary work to reinforce the cliffs so that homes could be built on them was suspended following protests from campaigners.
Developer, Living Quarter Properties Porth, has been given planning permission to build seven holiday homes on top of the cliffs above the beach.
Andrew Robey of the Save Whipsiderry Cliffs Group said he's not shocked by the collapse.
He said: "We have noticed there has been an increase in cliff falls and we have been trying to tell people. We have submitted a lot of evidence to show that the cliff is highly unstable.
"That has always been one of our concerns, and sadly we've been left with the situation of a significant cliff collapse at a beach which is beloved by many Newquay residents. I'm pretty angry and very sad."
The developers were given planning permission to build on the land by Cornwall Council.
They were also given a license to reinforce the base of the cliff with concrete by the Marine Management Organisation (MMO) and the Duchy of Cornwall granted access to the beach.
In September, the MMO stopped the developers from carrying out work to reinforce the cliffs until early 2024 following concerns.
In a statement, the MMO said it suspended the developer's licence for the cliff works so it could “conduct an independent geotechnical analysis of the cliff, to identify whether the works as licensed (including the existing conditions) are geo-technically sound in order to fulfil their purpose.”
The work had previously been put on hold temporarily after the Duchy of Cornwall — a private estate that funds both the charitable and private activities of the Duke of Cornwall, Prince William — withdrew the developer's access to its land.
Cornwall Council urged people to "stay away from the area for your own safety." It said it closed the steps down to the beach and the footpath surrounding the area following the incident.
"Be aware that with the steps closed, there is a risk of getting cut off by the tide if walking along the beach from Porth to Watergate," the council added.
Devon and Cornwall Police said the area has been cordoned off. It added a fence is being put up to make the area safe in case of further cliff falls.
Living Quarter Properties has been approached for comment.