Multiple emergency services were displayed to a major incident on Thorpe Bay seafront, near to Uncle Toms Cabin.
Reports came in on Sunday morning of two people being in distress in the water.
A Coastguard rescue helicopter was called to conduct a search of the water, with police, firefighters and paramedics all present at the scene.
An Air Ambulance also landed at the incident at Shoebury Common Beach.
Key Update: Two people have been rushed to hospital after their dinghy capsized. One is said to be in a “serious condition”.
The East of England Ambulance Service was dispatched at around 9.30am this morning, following the reports of two people being in distress in the water.
Southend Coastguard said it had received multiple 999 calls about the capsized dinghy.
RNLI lifeboats also helped the Coastguard to search for the two people in the water.
A Coastguard spokesperson said: “One of the two people was able to make it to shore on his own. The second was recovered from the water by the coastguard rescue teams.
“A Coastguard paramedic was winched down to assist and the casualty was taken to hospital by Helimed.”