Emergency services were called to an incident at the Shoebury Garrison nature reserve. 

Southend Coastguard was also requested to help but was eventually stood down after a person was treated by the ambulance service. 

Coastguard crew had been carrying out training exercises on Saturday morning before they were asked to attend a medical emergency at the nature reserve by police. 

This was partly because they had access to a defbrillator. 

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The coastguard arrived at the scene but was stood down by ambulance staff, who were treating a person inside an ambulance at the time. 

A coastguard spokesman said: "We wish the casualty a quick and full recovery."

The East of England Ambulance Service says the person was taken to Southend Hospital for treatment.