More than 100 people have been treated in hospital after a suspected chemical leak along the East Sussex coast.
Birling Gap beach was evacuated on Sunday after people reported breathing difficulties, stinging eyes and vomiting when a "mist" appeared.
Eastbourne District General Hospital says it has treated 133 people.
Investigations were under way into the cause of the "chemical haze", which was currently unknown, Sussex Police said.
The force said it believed it came in from the sea - previous incidents have involved something coming over from an industrial unit in France - but this has yet to be confirmed.
However, East Sussex Fire and Rescue Service said it was "extremely unlikely" that it was chlorine - the police said the effects, while uncomfortable, were not serious.
A police spokesman said the first report came in just before 17:00 BST where "up to 50 people had been affected by irritation to eyes and throats".
The first reports were from Birling Gap, but the plume of gas moved eastwards along the coast as far as Bexhill, police said.
As of Sunday night 133 patients were being "decontaminated" at hospital, East Sussex Healthcare NHS Trust said.
EDDIE MITCHELL
Coastguard rescue teams from Birling Gap, Eastbourne, Bexhill and Newhaven raced to help clear the busy beaches as visitors feared they had been struck by a chlorine leak.
Kyle Crickmore, who was at the Birling Gap beach with his family, said it emptied in 10 minutes after people began to feel unwell.
He described how a "foggy haze rolled in out of nowhere" and there was a "strong smell of chlorine in the air".
"It was definitely out of the ordinary considering it was a nice clear sunny day 10 minutes beforehand," he said.
"It was stupidly busy and it was a boiling hot day.
"It emptied in about 10 minutes, which was quite staggering considering the amount of people who were there."
EDDIE MITCHELL
Members of the public alerted emergency services, which triggered call-outs to the UK Coastguard, Sussex Police, South Eastern Ambulance Service and East Sussex Fire and Rescue Service, who said they were treating it as a "chemical incident".
The RNLI said that "possibly some kind of gaseous fumes" had drifted over and a significant number of people on cliff tops had been struck down with symptoms including irritation, sore eyes and vomiting.
Dan Sankey wrote on Twitter: "Beautiful afternoon at Birling Gap cut short by some weird mist, burning everyone's eyes which led to the beach and cliff being evacuated."
The beachfront is a popular hot spot for tourists and locals on bank holidays.
People living along the coast have been advised to keep windows and doors shut since the incident.
The police added that with another fine day expected for Bank Holiday Monday, thousands of people were expected to head to the coast again.
The situation would continue to be monitored, they said, "but it is believed that this was an isolated incident and is not expected to recur".
Please keep doors & windows closed following the #BirlingGap incident ow.ly/pttJ30eI69d
End of Twitter post by @chrisbaker999
Eastbourne councillor Kathy Ballard said: "We need to find out the cause, where did this come from, and to make sure that steps are taken so that it does not happen again.
"I have not heard of it happening before in this area."
The National Trust, which owns the land and has a cafe and visitor centre at Birling Gap, said it was aware of the incident and was working with the emergency services.
The hospital initially said it had treated 233 people, but later revised the number to 133.
