Police at the scene near Waddesdon, in Buckinghamshire.
It offers flight training for rookie pilots.
There are reports of multiple casualties.
Fire services also on social media: "Firefighters are now assisting other emergency services at scene of air accident near Waddesdon". The crash took place in a dense woodland. The manor said the crash did not happen at the site and there were no casualties at the manor.
A woman who lives nearby said she was out walking her dogs at the time of the collision. Staff at the manor are understood to have assisted at the scene of the crash.
RAF Halton, which is around 10 miles away, said no military aircraft had been involved.
However the notice added the air traffic zone surrounding Wycombe air park as well as gliding operation remained active.
"Wycombe Air Park can confirm at 12.09 today we were informed of an incident north-west of Aylesbury, involving two aircraft from Wycombe Air Park", the spokeswoman said. "Everyone is helping the emergency services".
Emergency services rushed to the scene, with fire officers launching a drone over the fallen wreckage in a desperate search for survivors.
In May, a man was left fighting for his life after the helicopter he was travelling in with two other men crashed at the site.
Two people were killed in each aircraft, which came down in woods near Waddesdon Estate, near Aylesbury, according to Thames Valley Police said.
South Central Ambulance Service said the incident had caused "a number of casualties".