Police and firefighters warned local residents to stay indoors and evacuated beaches on Britain's south coast on Sunday after reports of a "chemical haze" drifting inland and causing irritation to people's eyes and throats.
Sussex Police said the "haze" was "causing discomfort for people along the [Sussex] coast from Eastbourne to Birling Gap," urging people to avoid local beaches and remain indoors with windows closed if staying near the coast.
The force said the first reports came from Birling Gap around 5 pm (1600 GMT) that up to 50 people had been affected by something causing irritation to their 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," it said.
"Emergency services are treating people at Birling Gap and clearing the area."
Chief Inspector Bruce Mathews of Sussex Police said he was managing the force's response to "some form of irritable gas."
There was a "cloud" moving towards the Eastbourne and Bexhill areas of Sussex, Mathews wrote on Twitter.