Chemical and radiation experts have been called in following the unexplained death of a man found inside a tent in a field.
A passer-by discovered the body while walking in the Port Meadow area of Wolvercote, Oxford, at around 12.25pm today.
A strong chemical odour prompted the area to be cordoned off as specially-trained CBRN (chemical, biological, radiological and nuclear) officers were sent to the scene.
Thames Valley Police, Oxfordshire Fire and Rescue Service and South Central Ambulance Service were working together on the investigation.
Members of the public were being told to avoid the cordoned off area, and a number of local footpaths were closed, police said.
Sushila Dhall, chair of Oxford Pedestrians Association, told the Oxford Mail: "I tried to get onto the meadow but I was turned away and was told there had been a toxic spillage.
"There were people in full-body suits and police are stopping people from going onto the meadow."
Police said the death was being treated as unexplained but "at this time" there appeared to be no suspicious circumstances.
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