Witnesses reported seeing plumes of chalk dust rising from the scene when the incident happened at about 4pm.

The Coastguard, fire service and Sussex Police have been called to the area to check the extent of the fall and to see if anyone has been caught up in it.

Coastguard teams from Newhaven and Birling Gap have joined the hunt along with the search and rescue helicopter.

There are no reports of any injuries at this stage.

There are no reports of any missing people in the area but the Maritime and Coastguard Agency said a large scale search operation was launched due to the sheer scale of the cliff fall.

Kaimes Beasley, Duty Controller for the UK Coastguard said: "We will continue to search this area until we are satisfied, along with the other emergency services involved, that no one has been injured or trapped in this fall.

"We are advising beach goers to keep away from the scene and we are currently cordoning off the area in the interests of public safety.

"I cannot stress enough that this rock fall clearly shows how unstable cliff edges can be, so please keep your distance from cliff edges, at both the top and the bottom of the cliffs, at all times."

People have been watching the incident unfold from Splash Point on the seafront at Seaford.

One witness said: "It seems like a really big chalk fall.

"The dust that rose was so high it reached the top of the cliffs."

Another witness said: "All I saw was loads of police cars and fire engines turn up before they cordoned off the area and told people to stand back.

"There was a helicopter circling the area above and I could see the coastguard talking to people and warning them of the chalk fall."

Dean Barfield, from Seaford, said he saw the search operation start as a crowd of people formed to watch.

He said: "I wasn't sure what was going on but when I made my way to the end of the jetty I could see a pile of rubble in the sea at the bottom of the cliff."

The chalk cliffs along the coast have suffered several falls in recent years.

Nigel Cusack, group commander of East Sussex Fire and Rescue Service, said: "The situation now is that we have no reports of anyone else involved in this incident.

"There is a substantial collapse in the cliff which has fallen from within the boundary set by Lewes District Council. 

"We have used drones which have given us enough information so that we can scale back the operation."

Graham Easton, senior coastal operations officer for Area Eight in Kent and Sussex, said: "We are happy that we have given everything a good search and there is no final report of anyone caught up in this.

"A report was made that someone was near the collapse but we have spoken to him and we are satisfied that we have covered that.

"It is a dynamic cliff fall and is constantly eroding.

"If anyone is believed to be missing please contact the coastguard or the police."

Additional reporting at the scene by Josh Walton

More to follow