The unnamed neighbour said it was just "devastating".
"We just heard screaming and then just all the flames, we just tried to get the hose out to try and help."
Fire and Emergency southern fire shift manager Jill Higgison said emergency services received multiple calls about the fire on Vivian St in Burwood just before 10.45pm.
Three fire crews arrived to find the single-storey home well ablaze.
Higgison said some occupants inside at the time were able to escape the blaze but two people were unable to be rescued. She couldn't confirm their ages.
Police confirmed two people had died in the blaze.
A St John Ambulance spokesman said two people who survived the blaze were taken to Christchurch Hospital for treatment. They were in a moderte condition, he said.
One ambulance and two rapid response vehicles were called to the fire.
One fire crew has remained at the scene overnight to monitor hot spots, and a fire investigator was due at the scene this morning.
One Vivian St resident says they heard fire engines and sirens last night.
