LONDON -- An aircraft and helicopter collided in mid-air Friday northwest of London and a "number of casualties" were reported, authorities said.

Fire and ambulance services rushed to the scene at 12:06 p.m. GMT (7:06 a.m. EST) near Aylesbury in Buckinghamshire. Two ambulance crews, two ambulance officers and a rapid response vehicle were deployed, the South Central Ambulance Service said.

"We're aware of a number of casualties following an incident this afternoon," Thames Valley Police said in a tweet. "There were a number of road closures following the incident, which have now been lifted."

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The Air Accidents Investigation Branch said it was sending a team to the site of the accident, which is in dense woodland.

The crash took place near Waddesdon Manor, which is managed by the Rothschild Foundation, a family charitable trust, on behalf of the National Trust. The manor said the crash did not happen at the site and there were no casualties at the manor.

A nearby military base, RAF Halton, also said no military aircraft were involved.