Both aircraft involved in the mid-air collision near Waddesdon (helicopter and light aircraft), came from the Wycombe Air Park, near High Wycombe.
"Firefighters are assisting the other emergency services following a mid-air collision between a light aircraft and a helicopter near Waddesdon at 12.06pm".
South Central Ambulance Service said the incident had caused "a number of casualties".
The crash happened near the famous Waddesdon Manor in Aylesbury, England.
The crash occurred around half an hour after the latest closure was due to end.
It had flown nearly 14,000 hours as of May and had previously suffered substantial damage to its landing gear, propeller and engine following a crash at a Cornish airfield in 1993.
The aircraft suffered substantial damage to its landing gear, propeller and engine covering during a previous crash as it was taking off at Bodmin airfield in Cornwall in July 1993.
Response Emergency services have set up evidence tents
The Air Accidents Investigation Branch said it was sending a team to the site of the accident, which is in dense woodland.
The manor said the crash did not happen at the site and there were no casualties at the manor.
RAF Halton, which is around 10 miles away, said no military aircraft had been involved.
It offers flight training for rookie pilots.
Police chief Rebecca Mears said she could not yet give out the identities of the victims.
SEVERAL people are feared dead after a plane and helicopter collided in mid-air near a Buckinghamshire manor house this afternoon.
Staff from the country estate helped direct emergency vehicles and a huge cordon has been put in place.