The
coastguard's search helicopter was sent from RAF Wattisham to the
scene, one mile east of the harbour near South Foreland lighthouse.
A Dover Coastguard spokesman said: "We have a witness who
saw a rider drive deliberately towards the cliff edge. We are taking
it very seriously.
"We have found tyre tread marks at the scene. Whether the
rider meant to drive over the edge is yet to be ascertained.
"The bottom of the cliff is still underwater as the tide is
still high but it is ebbing away. We may have to wait a while longer
before we can find anything. An ambulance is on the scene and the
police have been notified."