Most of Spark's South Island broadband and landline network is hanging by a thread.

A cable running along the island's east coast was badly damaged by this morning's 7.5 magnitude earthquake, leaving South Islanders' connections relying on the Western cable, which runs from between Blenheim and Christchurch through Greymouth.

While a few hundred North Canterbury households were back online this evening, a further 1700 Spark customers had no access to their home broadband at 6pm, a spokeswoman said.

The fibre cable connecting Kaikoura to the national broadband and phone network had been severely damaged.


It ran along SH1 and was severed at multiple points to the north and south of the town.

The spokeswoman said Kaikoura's cable was so badly damaged it would likely take weeks to get the town's residents back online.