A temporary foot-and-mouth control zone has been set up on the border of East and West Sussex, the government says.
Animal movements are restricted in the control zone
The 3km (1.8 mile) zone was put around premises near Haywards Heath as a precautionary measure after clinical signs of the disease were found.
The Department for Environment, Food and Rural Affairs said laboratory tests were being carried out on cattle.
Movements of animals to and from premises, including into or out of the zone, are not allowed.
All livestock owners should examine their livestock twice a day, Department for Environment, Food and Rural Affairs (Defra) said.
The temporary zone is expected to be in place not more than a few days - until lab results are available and the disease situation clearer.
The disease has been confirmed in cattle at eight farms in Surrey since August.