Power is starting to be restored after the South Island was hit by a major power cut this morning.

Mainpower says power to areas of North Canterbury affected by this morning's widespread outage is now restored.

The power supply to Kaikoura was still being restored.

The electricity supply was disrupted from Timaru to the top of the South Island, including the West Coast from just before 11.30am.

Power is being gradually restored to more than 50,000 customers in Christchurch.

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Traffic was earlier thrown into chaos when nearly three dozen sets of traffic lights went out across the city contributing to a four-vehicle crash at the intersection of Marshland and Prestons Rds

A Transpower spokeswoman Rebecca Wilson said a fault in the Twizel area suddenly cut electricity to a wide area across the island this morning.

Wilson said the widespread blackout was the result of a "frequency event".

"A frequency event is when power drops below its normal frequency it starts to disconnect customers to protect the system," she said.

Orion spokeswoman Linda McGregor said more than 50,000 customers were affected because of a problem with a Transpower transmission line supplying the city from Twizel.

Power went out at 11.29am.

The New Zealand Transport Agency tweeted that the outage affected up to 35 sets of traffic lights this morning.

Motorists were advised to follow the give-way rules and take care using intersections.

The Hurunui District Council also asked people throughout the district to conserve water as all the water pumping stations were unable to operate.

It said no water would be pumped until power was restored.