Over 230 people have sought medical help for breathing difficulties, vomiting and stinging eyes following a suspected gas leak near Beachy Head near Eastbourne on Sunday.
Emergency services evacuated the popular beauty spot after dozens of people basking in the bank holiday weekend sunshine complained of stinging eyes and sore throats after a "mist" appeared on the beach.
Eastbourne District General Hospital said it has treated 233 people, where they are being 'decontaminated' East Sussex Healthcare NHS Trust told the BBC.
Witnesses claimed there was a distinct and pungent smell of “chlorine” in the air at the East Sussex site, with one saying it 'stung their noses.'
People have been warned to stay away from the area as Coastguard UK confirmed they have been ushering people from the beach.
Residents have also been advised to keep all their doors and windows closed.
East Sussex police have confirmed they are investigating the incident with the source of the "haze" and the irritation remaining unclear.
A statement from the force said the first report came from Birling Gap where up to 50 people had been affected by "irritation to eyes and throats".
"This seems to have been caused by an unknown haze coming in from the sea, but the source has not yet been established.
"Emergency services are treating people at Birling Gap and clearing the area."
Witness Mark Battershill was at the beach with his wife and two children aged 5 and 11.
He told the BBC: "My eyes were really streaming. My wife had the same problem, and my daughter."
Police have issued a further warning that the "haze" appears to be shifting eastwards towards Hastings.
The South East Coast Ambulance Service said anyone affected should wash with copious amounts of water.
"If you have any serious concerns then you should seek medical advice.
"People are urged not to go to hospital unless an absolute emergency."
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