There were 275 passenger in the flight flying from Heathrow to Hongkong heared an emergency announcement in automated female voice that we need to make an emergency landing on water. Cabin crew members ran down to aisles to announce that it was by mistake, pilot hit the wrong button hey were so close together. People were scared and thinking that they all are going to die.Passengers on the flight never been in a situation in which the plane they were on was about to crash. British airways apologies to passengers on the flight for causing them undue distress.