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A quayside path was cordoned off by police amid reports a man fell in the water.
Officers were called to St Mary's Island in Chatham just after 9.30am, close to where the Chatham Maritime Food and Drink Festival is being held.
An air ambulance joined a large number of emergency services at the scene, and a green tarpaulin was used to screen off part of the path.
Police say the man has been taken to hospital for treatment.
The Maritime Way bridge, which leads to St Mary's Island, was cordoned off but reopened at about 10.45am.
Emergency services - including the Coastguard - have now left the scene.
A spokesman said: "We were called at 9.30am to a report of a concern for the welfare of a person seen in water near Barrack Road, Chatham.
"Officers are in attendance and a man has been taken to a local hospital for medical treatment."
The three-day Chatham Maritime Food and Drink Festival, which concludes today, is continuing to run.