Animal health officials are investigating a suspected foot and mouth outbreak on a pig farm near Feltwell in west Norfolk.
A 10km control zone preventing the movement of any susceptible animal into or out of the area has been enforced.
Foot-and-mouth disease is a highly infectious, frequently fatal ailment that affects cloven-footed animals such as cattle, sheep and pigs.
A spokesperson for the Department for Environment, Food and Rural Affairs said that while preliminary testing did not indicate the presence of disease, “further work is now under way to fully rule it out”.
The last major foot and mouth outbreak in the UK took place in 2001 when more than 6 million farm animals were killed to try to contain the virus. The first cases in that outbreak were reported in pigs.
A more recent outbreak in 2007 did not spread beyond a handful of farms.