People on the south coast of England have been warned to stay away from beaches and to keep doors and windows closed due to a chemical 'haze' in the area.
Emergency services issued the warning near the East Sussex coast after up to 50 people complained of irritation to their eyes and throats.
Sussex Police said: "This seems to have been caused by an unknown haze coming in from the sea, but the source has not yet been established."
East Sussex Fire and Rescure Service said the "chemical incident" was ongoing.
The first calls were made to the emergency services just before 5pm.
Police said the source of the haze has not yet been established.
A spokesman said: "Emergency services are treating people at Birling Gap and clearing the area.
"People living along the coast in the area have been advised to keep doors and windows shut and to move away from the Birling Gap area in particular."
Some sort of chemical incident at Birling Gap, eyes are streaming and there's a strong smell of Chlorine in the air pic.twitter.com/rIPMaS58m4— @Kyle_Crickmore (@Kyle_Crickmore) August 27, 2017
The RNLI said that "possibly some kind of gaseous fumes" had drifted over the scene and a significant number of people on cliff tops had been struck down with symptoms including irritation, sore eyes and vomiting.
Fears from the coastguard that people could be trapped on the beach saw the RNLI launch all-weather lifeboats from Eastbourne and Newhaven to the Birling Gap area.
Birling Gap some weird gas leak. People crying. Ambulances called. Don't go to Birling Gap at the moment— Sameer Jadhav (@samkoyna) August 27, 2017
There was a doctor on board the Eastbourne lifeboat.
A spokesman said: "We have been checking along the shoreline to try and ensure that everyone is safe."
Beautiful afternoon at Birling Gap cut short by some weird mist, burning everyone's eyes which led to the beach and cliff being evacuated— dan sankey (@electroblankets) August 27, 2017
He said a "plume" had drifted across the area bringing "some sort of substance" with it which seemed to affect a number of people.