The strain can be fatal if it is passed on to humans but experts said the outbreak was being contained and posed little danger to people.
A spokesman for Bernard Matthews, which runs the farm in Holton, said none of the affected birds had entered the food chain and there was no risk to health.
The 159,000 other turkeys on the farm will now have to be slaughtered.
The Department for Environment, Food and Rural Affairs and the European Commission carried out virus tests at laboratories in Weybridge, Surrey.
A three-kilometre protection zone and a 10km surveillance zone will be set up around Holton, which is approximately 27km south-west of Lowestoft.
It is the first case on a UK commercial farm of an H5N1 infection. The strain has killed 164 people worldwide - mainly in south-east Asia - since 2003.
However, the virus is not thought to be able to pass easily from human to human at present.
So far, all those who have been infected worldwide have come into intimate contact with infected birds.
Vaccinations
Fred Landeg, Britain's Deputy Chief Veterinary Officer, said an investigation was under way but the most likely source of the outbreak was wild birds.
He told BBC News that vaccinations for poultry were not currently being considered.
"There are a number of problems with vaccination in that it takes about three weeks to get immunity."
DEFRA CONTINGENCY PLAN
Full document [372KB] Most computers will open PDF documents automatically, but you may need to download Adobe Reader. Download the reader here
Mr Landeg said the turkeys at the farm had been too young to enter the food chain and no birds or produce had moved off the site.
Dr Maria Zambon, from the Health Protection Agency, said farm workers who had come into contact with infected birds, and those involved in the culling process, would be offered the anti-viral drug Tamiflu as a precaution.
She stressed that nobody had developed symptoms of bird flu following similar outbreaks among farm birds in continental Europe.
Vets were called to the Bernard Matthews farm on Thursday night.
The company said it was confident the outbreak had been contained and there was no risk to consumers.
National Farmers Union president Peter Kendall told BBC News 24 the priority would be eradicating the outbreak.
"[We will be] making sure we get the message across about how well this will be managed and controlled.
"We're encouraging all farmers to be incredibly vigilant, look at their flocks carefully and we do need to reassure consumers that this is not an issue about the safety of poultry - it's completely safe to eat."
Defra has revoked the national general licence on bird gatherings and bird shows and pigeon racing will not be permitted.
Detergent
Professor John Oxford, a virologist at the London Queen Mary's School of Medicine and Dentistry, said he was confident the outbreak could be contained.
He said: "I don't think it has made any difference as a threat to the human population. The most likely explanation is that a small bird has come in through a ventilation shaft.
"One good thing about this virus is that it's easily destroyed. You can kill it with a bit of detergent."
Dr Oxford also said that while four strains of the H5N1 virus have been identified so far, all are deadly to birds and show potential of being harmful to humans.
He said that identifying the particular strain found in Suffolk will help scientists work out how the disease is moving around the world.
HAVE YOUR SAY The people most at risk are farmers and their families
Andrew Olgado, London
Send us your experiences Community in shock
In May last year, more than 50,000 chickens were culled after an outbreak of the H7 bird flu in farms in the neighbouring county of Norfolk.
One member of staff at the farm contracted the disease and was treated for an eye infection.
In March 2006, a wild swan found dead in Cellardyke, Fife, was found to have the H5N1 strain of the virus.
For more information call the Defra Helpline on 08459 33 55 77
Vue colorisée du virus H5N1 par un microscope électronique.
 La présence du virus '''H5N1''', responsable de la grippe aviaire qui a déjà sévi en Asie, a été confirmée dans une ferme à Suffolk, expliquant ainsi la mort de 2 600 dindes.

Le ministère de l'environnement, de la consommation et des affaires rurales (DEFRA) a procédé à plusieurs tests afin de déterminer son impact après que plusieurs dindes dans la ferme de Bernard Matthews, aient présenté les symptômes de la grippe aviaire : les tests effectués pour confirmation se sont donc révélés positifs. 

Par application du principe de précaution, 159 000 dindes devraient être prochainement abattues.

Le Conseil de l'Europe a édicté une directive stipulant qu'une zone de protection d'un rayon de trois kilomètres doit être mise en place autour de l'installation incriminée. Il a aussi ordonné une zone dite  dans un rayon de 10 km, où la vente des oiseaux au marché est interdite. L'eau utilisée par les animaux domestiques doit être séparée de celle réservée aux oiseaux sauvages. Les déplacements à pied sont limités. La surveillance des symptômes des oiseaux infectés est accrue. Les oiseaux ne pourront pas être transportés sauf pour être abattus.

Les services restent confiants et estiment que l'épidémie a été contenue tout en recommandant à la population plus de vigilance.