An Angolan military plane has crashed after take-off from the central city of Huambo killing at least three generals, the state news agency Angop says.A Huambo-based journalist told the BBC that 30 of the 36 passengers had died - but no official toll has been released.It is not clear what caused the accident, but most of those on board are believed to be air force officers.Correspondents say the aircraft was an Embraer jet recently purchased by the army to transport top officials.Journalist Manuel Vieria told the BBC's African Service that there were six survivors. Portugal's Sol newspaper is also reporting that 30 passengers were killed.The paper quotes a survivor in hospital as saying that the accident happened so fast it was difficult to know what the problem was, but the pilot seemed to be aware that there was a technical fault.Portugal's news agency Lusa said the accident happened at about midday local time (11:00 GMT).