Residents included some suffering mental illness and medical conditions such as diabetes.
The smoke alarm then sounded and the residents evacuated.
A neighbour alerted emergency services while another turned off gas bottles on an outside wall leading to the kitchen area.
One of the residents remained and used a garden house to help contain the fire in the room until firefighters arrived.
"The firefighters smashed a window and then a door to get inside and then dragged the burning mattress out," he said.
The residents gathered outside and were checked over by a St John Ambulance crew.
Another resident said no one was living in the room and the door was supposed to be locked. He had not seen anyone leaving the room and was unsure how the fire started.
He had gone through the room yesterday morning and cleaned up the ashes and was airing out the room.
He suspected some one who was not a resident at the guesthouse had gone in the room unnoticed and started the fire.
The property owner arrived at the house yesterday just before 1pm to inspect the room but declined to comment.
A fire safety inspector was thought to have been to the scene but could not be contacted by deadline.
Meanwhile, several residents on Riverview Rd in Kerikeri called 111 about 1.45am yesterday after being woken by a fire.
Kerikeri fire chief Les Wasson said someone had decided to burn a pile of vegetation in the early hours of the morning, and it was the sound of bamboo popping that woke the neighbourhood.
The property owner blamed neighbours for lighting the backyard blaze, which was extinguished by firefighters.
