The huge sinkhole, named Souter Hole, first appeared in 2003 and has continually grown to around 40ft while a small beach formed at the bottom.
Experts at the National Trust say sinkholes form when limestone is dissolved by groundwater flowing through spaces and cracks in the rock, which in turn creates gaps below the surface.
Eventually, the land surface will collapse into these void and creates a sinkhole.
Souter Hole has now expanded to 40ft and is expected to continue growing due to a combination of erosion by rainwater from above and wave action which has broken through the cliff below.
Teams at the National Trust, which manages the cliff path around the hole, say sinkholes are not uncommon in coastal areas like Whitburn.
A spokesperson at the Trust said: "Sinkholes are most common in areas with water-soluble bedrock including limestone, such as the Magnesian Limestone which forms the cliffs between South Shields and Sunderland."
Some sinkholes can be caused by human activity, while others from naturally, experts say Whitburn’s sinkhole is a combination of both.
The Trust added: “In the past, the area was an industrial site, featuring a papermill, colliery and quarry. When quarrying finished, the quarry was filled with inert rubble/soil type material.
"The sea eventually punctured a hole in the limestone cliff that was left intact and washed this material out.”
A secret beach has also appeared at the bottom of the hole as specialists say its due to the action of waves which creates sand from rocks that are broken down by weathering and erosion.
Eventually, it is thought the cliffside will collapse in time – but it could take several years.
The National Trust spokesperson said: "It’s difficult to predict exactly what will happen, or when, but the cliffside exposed to the sea will probably erode to the point of collapse in time, turning the sinkhole into a small cove. This could take several years.”
The National Trust are reminding visitors to ‘stay safe’ while at Whitburn Coastal Park.
Eric Wilton, General Manager at the National Trust said: “We want all of our visitors to have an enjoyable, relaxed and safe visit to Whitburn Coastal Park.
“By its nature the coastline is constantly changing, with some areas particularly prone to erosion and landslips.
"This sink hole first appeared around 2003 and is regularly surveyed. We have put up fencing and warning signs around this sink hole, which is away from the main path running along the cliff tops of The Leas and Whitburn Coastal Park.
"There are warning signs at key points along the cliff edges, as well as visitor information panels in each car park."
"We'd urge people to take a moment to look at these signs, and to stick to the main paths to keep themselves, their children, and their dogs safe."