A police dog tracked his trail but then lost it - it's thought the offender may have escaped by vehicle.
The couple are being supported by police and comforted by neighbours.
Investigators are asking the community to help them find the perpetrator.
He is about 170cm tall, of medium build and has been described as possibly Maori or Pasifika.
He was wearing a lightweight dark training jacket over a black hoodie, had dark trousers, dark running shoes, and was concealing his face with a pale-coloured scarf.
Anyone with information or who operates CCTV in the area is asked to contact Constable Roger Carran at the Christchurch Central Police Station on 03 363 7400.
Alternatively, details can be supplied anonymously to Crimestoppers on 0800 555 111.