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Lines company Orion said that in some cases, power may not be restored for up to five days.
Areas affected were mostly in the rural region west of Christchurch, where outages were caused by trees or branches falling on power lines.
Power had been restored to most of urban Christchurch, but half of Orion's major rural substations were still out, chief executive Rob Jamieson said.
"Last night 28,000 customers were without power. As of 4pm we have managed to restore power to approximately 50 per cent of affected customers," Mr Jamieson said.
"Our crews are working as quickly as they safely can. However, there is extensive damage and so customers need to prepare for the possibility of extended power cuts. If a customer is without power at 4pm today they should prepare for a night without power. In some cases, power could be out for up to five days."
The extensive power cuts and damage to irrigators prompted a call for generators to help farmers over the next few days.
Federated Farmers were asking anyone with spare generators available to get in touch, as farmers would be willing to travel to get them.
Some households in Ashburton are also facing a second night without power tonight.
Lines crews from local power network EA Networks were unable to restore power today because of dangers from ongoing high winds, said district network manager Brendon Quinn.
Power was off in most areas east of State Highway 1, and pockets in the Eiffleton and Three Springs area might not be reconnected until Saturday.
The Lewis Pass and Haast pass are both closed due to flooding, and State Highway 94 from Te Anau to Milford Sound is closed due to fallen trees and avalanches.
In Wellington, gale-force winds dragged an anchored 20,000 tonne logging ship across the harbour this morning, and tore a yacht from its moorings in Evans Bay.
Last night high winds fanned fires in the Ashley Forest, west of Amberley, and in a plantation west of Kaikoura, with many other small fires being caused by downed power lines and lightning strikes.
The Fire Service also responded to weather callouts in Wellington and Wairarapa, including trampolines blown away and roofing iron blown off.
High winds caused problems on the roads in Wairarapa, with three trucks and a campervan blown over today.
A traffic diversion after a truck rolled on State Highway 2 near Carterton this afternoon had to be moved after a fallen tree blocked the diverted road, police said.
Gales gusting up to 120km/h caused power cuts to 2500 Wairarapa customers last night but about 2000 were restored today. The rest were expected to be reconnected by tonight.
Powerco Network Operations Manager Phil Marsh said field staff had worked through the night making steady progress in challenging conditions.
"There are currently around 500 properties spread around rural parts of Wairarapa without power and we expect to restore the majority of supply by the end of the day, barring more severe weather," Mr Marsh said.
A strong wind warning will remain in place tonight for Wellington, Wairarapa, Hawkes Bay and Gisborne.
Metservice forecaster Oliver Druce said the worst of the weather had moved off the South Island, and would be easing in Wellington and Wairarapa by early morning.
Strong winds would continue in Hawkes Bay and Gisborne through tomorrow.
Heavy rain was also expected in the Tararuas, Mt Taranaki, the central North Island and eastern Bay of Plenty.
