The swimmer had tried to navigate the 27 mile stretch of water between England and France, but got into difficulty reports suggest.
Search party underway: The person went into the water around midday this Bank Holiday Monday but never surfaced.
A friend rang the emergency services after getting worried and the Kent coastguard were dispatched.
A coastguard spokesperson said: “At around 12.10pm today, HM Coastguard received a call from a member of the public with information that their friend was swimming unaccompanied to Calais from Dover.
Search party underway
“Coastguard rescue teams from Deal and Langdon, an RNLI lifeboat from Dover and a coastguard search and rescue helicopter from Lydd have been sent.
“Vessels in the area have been asked to keep a sharp lookout and Kent Police, Dover Port Police and Dover Port have been informed.”
According to the UK Met Office, air temperatures in Dover during the afternoon were about 17C (62.6F) and wind speeds were up to 10mph.
It is understood a total of eight people have died trying to swim the Channel. Susan Taylor, 34, was swimming the 21 miles to raise money for charity when she fell ill and died a mile from the French coast in July 2013
The search will continue into the night and tomorrow.
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