The pilot remonstrated with some of the attacking ravers
An air ambulance crew and their helicopter were pelted with cans and bottles as they tried to help an injured man at a rave in Norfolk.
Police condemned the "reckless and irresponsible behaviour" which put the crew and their vehicle at risk at Feltwell, near Thetford.
The crew, who were unhurt, were called while police were on site on Sunday.
Officers made several arrests and seized equipment at the rave, which was attended by about 500 people.
A rave at nearby Bodney on Saturday night had been broken up by police, with organisers and attendees moving on to the second site.
'Very worrying'
Supt Nick Davison said the "foolish" actions had potentially serious consequences.
"Not only was the safety of ambulance staff put at risk, but the fact that the helicopter was targeted is very worrying," he added.
Our crews are dedicated to saving lives so it's inexplicable to us that they would be threatened in this way
Simon Gray East Anglian Air Ambulance
"Had the air ambulance been damaged, then a vital resource for the whole of East Anglia could have been lost."
Simon Gray, managing director for the East Anglian Air Ambulance, which has two helicopters, said he was horrified by the events.
Dr Richard Browne and paramedic Dan Cody, supplied by the emergency medical charity Magpas, were trying to help a man who had fallen from a height and injured his leg and back.
The patient was given "accident and emergency-level" assistance and taken to hospital by land ambulance.
"Our crews are dedicated to saving lives so it's inexplicable to us that they would be threatened in this way," said Mr Gray.
"Equally, the aircraft is funded purely by the hard work of the charity's many supporters, who work tirelessly so that we can keep it flying.
"Our pilot remonstrated with some of those throwing bottles and fortunately none of the crew was harmed and the aircraft was not damaged.
"The outcome could all too easily have been very different."
More than 150 vehicles were stopped during the operation, with arrests made over suspected vehicle offences and drink driving.
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