The cause of the chemical “haze” which descended on the Sussex coast on Sunday remains unclear, police have said.
The cloud was “very unlikely” to have floated over from northern France, and suggestions it came from a ship could not be confirmed.
Some 150 people required treatment for stinging eyes, sore throats and vomiting, but the effects of the unknown substance were “mostly minor”, Sussex police said.
Video, above, shows crowds on a beach reacting to the cloud.
In the past, chemicals have drifted across from European industrial units, but weather models indicate this was not the case on Sunday, according to the Met Office.
Forecaster Jay Merrell suggested a vessel in the English Channel may have been responsible for the noxious haze, but stressed nothing conclusive had been proven and that inquiries continue.
Bob Jefferey, of the Royal National Lifeboat Institution (RNLI) Eastbourne division, said it would be business as usual, the Press Association reported.
He said: “Whatever it was, it smelled like burnt plastic. It hung about and didn’t move yesterday because there was no wind. The cloud seems to have dispersed today though.
“The hospital has downgraded the threat to pretty much non-existent now.”
Jefferey added that five people had to be rescued from rapidly rising tides yesterday, and urged beach-goers to watch sea levels.
People along the shoreline from Eastbourne to Birling Gap, near Beachy Head, were advised to close windows and doors on Sunday, but have been told it is now safe to open them.
Kyle Crickmore, who had been enjoying the bank holiday weekend sunshine at the beach at Birling Gap with his family, tweeted: “Some sort of chemical incident at Birling Gap, eyes are streaming and there’s a strong smell of chlorine in the air”.
Dan Sankey added: “Beautiful afternoon at Birling Gap cut short by some weird mist, burning everyone’s eyes which led to the beach and cliff being evacuated.”
Sussex police said: “Neither the gas nor its source have been established, but agencies are continuing to investigate and have not ruled out either on-shore or off-shore locations, although it does appear that it did sweep in from the sea driven by on-shore breezes.
“However, weather models suggest that an onshore source in northern France is very unlikely.”
Public Health England said anyone still suffering effects from the fumes should wash irritated areas with soap and water.