A cluster of whooping cough cases have emerged in a Christchurch household

Health New Zealand is aware of eight cases of the disease in the area - but says it's not considered an outbreak.

Almost half of the country's cases identified in the past week were from Canterbury, with nine in Wellington, Wairarapa and Waikato.

The disease typically spreads more in the cooler months, when people spend more time indoors.

Medical officer of health Dr. Cheryl Brunton says there's no immediate concern to Christchurch residents, because the cases are all from the same family.

She says there's been a gradual rise in reported cases since late last year - though numbers are relatively low.