Bird flu has been discovered on a second farm in Lincolnshire within one month.
The H5N8 strain of avian flu was found in a flock of turkeys at Low Farm in Fulstow on January 16, with up to 6,000 birds affected.
A number have died and the remaining live birds are being humanely culled.
As previously reported, the same strain was confirmed at a farm in nearby Tetney, close to Louth on December 16, 2016.
The Department for Environment, Food and Rural Affairs does not believe the two cases are directly linked.
Despite this, a full investigation is underway to confirm this.
A 3km protection zone and a 10km surveillance zone have been put in place around the infected premises to limit the risk of the disease spreading.
Public Health England has said the risk to the public from the virus is very low.
The Food Standards Agency has said that bird flu does not pose a food safety risk for UK consumers.
Chief veterinary officer Nigel Gibbens said: “We have taken swift action to limit the risk of the disease spreading with restrictions in place around the affected premises. A full investigation is underway to determine the source of the infection.
“This finding reminds us that we must all be vigilant for signs of disease and take steps to minimise the risk of birds catching the disease from wild birds – either directly or through the environment.
“This means complying with the legal requirement currently in place to house birds or otherwise keep them separate from wild birds and following strict biosecurity measures to minimise the risk of avian flu spreading via the environment.”