The fire is still not contained, he said, leaving firefighters with "quite a lot of work to do".
Updated data shows the fire is now spread across 2400 hectares, with a perimeter being reassessed at 33km.
Mitchell said that the female firefighter hospitalised yesterday with dehydration was recovering well.
Tasman Mayor Richard Kempthorne reminded locals that they face a long recovery.
Firefighting efforts on the ground will be ongoing for "at least a month, mostly likely longer", he said.
Hi everyone, if you have been affected by the fire and need assistance please come and visit our Richmond Civil Defence...
Posted by Nelson Tasman Civil Defence on Tuesday, 12 February 2019
Authorities are today still working on plans to assess when evacuated residents of the areas known as the valleys can go back home.
It was a complex task, with about 200 properties involved, Civil Defence controller Roger Ball said.
There is no timeframe yet but there will be a community meeting tonight at 7pm in Hope, where the valleys re-entry will be the top of the agenda.
Meanwhile, police investigations into the suspicious and unrelated Rabbit Island and Nelson city fires are continuing.
Acting Tasman district commander Inspector Zane Hooper said staff were actively following up inquiries.
Hooper said there have been no reports of looting, but reminded people to stay away from cordons.