Eyewitnesses described seeing small slips as early as 10am but the main landslide occurred at mid-day with tonnes of rock crashing onto Seaham Hall Beach.
Brian Weatherall, Durham County Council’s drainage and coastal protection manager, has explained that coastal engineers will be inspecting the area.
He said: “We have been made aware of the landslide onto the beach at Seaham.
“Our coastal engineers will be visiting the site to assess the area.
“We would encourage everyone to stay away from the cliff edges and avoid the area where the landslide has occurred as the material may be loose and unstable.”
An eyewitness who captured footage of the landslide described how loud it was when the cliff collapsed.
They said: “People need to be mindful of the erosion along the cliffs especially when it comes down in that sheer mass.
“A lot of people travel here to go sea glass hunting so always have their heads down, not noticing what is going on around them.
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“I was actually having a quick sea dip when I noticed the first slide.
“Then afterwards over around two hours later there was quite a bit of movement.
“The sound was insane, this happens a lot with bad weather but I’ve not seen a landslide on that scale before.”