Police were called to the farm because of "safety concerns"
A man has died and seven police officers are in hospital along with three ambulance staff after a noxious substance was found at a Surrey farm.
Police were called to Burpham Court Farm in Guildford at about 0100 BST where they found a man in his 50s suffering from breathing problems.
Paramedics tried to resuscitate him but he was pronounced dead at the scene.
Emergency crews were taken to the Royal Surrey County Hospital as a precaution, and are expected to be released later.
A police spokesman said officers were called to the farm - a rare breeds conservation centre - because of "safety concerns".
"Following a call to Surrey Police during the early hours of 28 May, officers arrived at Burpham Court Farm, Guildford, regarding a concern to safety," he said.
"One person - a man in his 50s - was found at the premises and it was apparent some sort of noxious substance was present at the scene which is currently being investigated."
A helicopter was scrambled over the scene as police investigations continued on Thursday afternoon.
The police officers and ambulance staff were being observed in hospital but were not injured, emergency services said.
The three ambulance crew members - a paramedic, technician and emergency care support worker who tried to resuscitate the man - underwent decontamination procedures.
Surrey Fire and Rescue Service said they were called to a potential domestic dispute.
A spokesman for Surrey Fire and Rescue Service said the substance could have been some kind of poison, possibly a pesticide or insecticide.
A source later revealed it was believed to be rat poison.
Firefighters remained at the scene in Clay Lane on Thursday afternoon.
One neighbour who lives in Clay Lane said: "There are forensic officers everywhere - police are clearly taking this seriously."
The former dairy farm is understood to have been turned into a conservation centre and tourist attraction in recent years.
The 76-acre riverside site is home to a variety of rare breeds and wildlife and parts of the farm date back to the 1600s.
Recent owners include the Duke of Sutherland and Paul Getty, but the farm's website states that it is now tenanted by Bob and Margaret Dearnley.
No-one was at the site to comment.
Police and fire crews remained at the farm carrying out investigations