People are being warned to stay indoors and keep windows shut in parts of Sussex amid reports of a noxious odour.
The odour, described as "like burning plastic", was first noticed in the Ridings area of Seaford at around 6pm.
Some people have complained of stinging eyes and feeling sick.
Police are working with other agencies, including the Coastguard, East Sussex Fire and Rescue Service and Lewes District Council, to try to determine the cause of the smell.
In August a toxic 'haze' caused discomfort to people in the Birling Gap area, but the Seaford incident is not currently being linked to this.