500 emergency service personnel will test their skills in a major exercise at Sydney International Airport.

The mock emergency will test the response to a serious incident where an aircraft experiences engine failure, resulting in multiple deaths and injuries.

The operation is six months in the making and will commence at midday and end at 4pm.

Those in the area this afternoon are being told not to panic if they see a large number of emergency vehicles.

Emergency Services Minister Troy Grant says more than 20 agencies and organisations will take part.