Detective Inspector Stan Brown told media today Ms Mason was known to have mental problems and Alyssa's parents took her into their home "out of the goodness of their hearts''.
"As far as we know Skye left Alyssa's family home without any baby clothes, toys food or blankets with her.
"The temperature last night was very cool and it's likely to be colder tonight with rain also forecast.''
Police have taken the unprecedented step of alerting the public about the kidnapping by putting information about the little girl on electronic motorway signs between Auckland and Wellington
As far as police know, the pair are on foot, but they could be have been taken in a car somewhere by an acquaintance of Ms Mason.
When they were seen last night, police said people who saw them observed that Ms Mason was caring for Alyssa "as if she was her own child''.
Police, including the Specialist Search Group (SSG) and the Air Support Unit (Eagle), searched in the Glen Eden area overnight until they were stood down at 3.30am.
Mr Brown said it was vital that anyone who had seen or had contact with Ms Mason or Alyssa since yesterday afternoon and particularly since about 10pm last night, called 111.
The police search operation was back underway today with SSG back in the Glen Eden area and Eagle had again been requested to help.
Northern police spokeswoman Noreen Hegarty told APNZ Alyssa's parents were "understandably frantic''.
'It's very important that we get reported sightings of one or both of these people so we can find Alyssa.''
Alyssa is described as a stocky child with sandy blond hair and blue eyes. She was wearing pink and white striped pants, a green and white T shirt and gum boots.
Ms Mason is described as Caucasian, 160cm tall, and of slim to medium build with golden-brown long hair. She was last seen wearing black adidas pants, a pale blue shirt with dark patterns, gloves, and white adidas shoes.
