About 24,000 people in Christchurch are still without power. Civil Defence says half these should have power restored by Sunday.
Lines company Orion says the Brighton substation is operating again, which means customers will start being reconnected from late on Thursday.
The company says there are faults on every single underground cable leading out of the substation, and that repair work is top priority.
Meanwhile, Civil Defence says it has more than 200 building evaluation teams, including 400 welfare staff and 50 search and rescue staff, visiting homes in the eastern suburbs.
The teams are prioritising building evaluations, portaloos and chemical toilets to the badly-hit eastern suburbs and areas of greatest need.
Civil Defence says building inspectors will have evaluated all the high-priority buildings in the eastern suburbs by the end of Saturday.
Land Search and Rescue teams have checked 56,000 houses around the western suburbs and say about 60% are still occupied.
National Civil Defence controller John Hamilton says chemical toilets and portaloos are being distributed to the areas of greatest need.
Eighty-six extra portaloos were being delivered to Avonside and Dallington and a further 120 on Friday for eastern suburbs.
About 1200 more portaloos are due by the weekend. Chemical toilet distribution has also begun in the eastern suburbs.
Water warning, transport resumes
Christchurch's Medical Officer of Health, Ramon Pink, says rivers, seawater and ponds must be treated as contaminated and fish and shellfish are also at risk of contamination. Residents are still urged to boil water, whether it is from mains or tankers.
Limited public transport services were beginning again in Christchurch on Thursday. Services are not operating in the hill suburbs and in badly damaged areas in the east. There is no charge for bus and ferry journeys for the next two weeks.