Hundreds of firefighters are battling to contain the blaze which broke out Wednesday afternoon, seven years to the day of the devastating fires of 2017.
The fire grew from 100 to 630 hectares overnight and the smoke plume is now visible from space.
Christchurch and Selwyn have been in a state of emergency since late last night.
A hundred and ten homes have been evacuated, and evacuation centres are open in Halswell and Lincoln.
No houses have been destroyed, but the fire has breached the edge of Christchurch Adventure Park.
In a separate incident this morning, a grass fire which broke out in Rolleston, about 30 kilometres from the Port Hills fire, has now been contained.
Reporter Tim Brown spoke to Charlotte Cook.
