An elderly mental health patient who murdered a pensioner at her Christchurch home with an axe says he's "extremely sorry that I've done what I did" - but doesn't recall the event.

A British scientist says it's concerning Prime Minister Christopher Luxon has dismissed him and other climate scientists as "worthies" for raising concerns about plans to lower NZ's methane emissions target.

Motorists are warned to drive to conditions due to ice, fog and snow in parts of Otago, Southland and Canterbury. There have been minor crashes in Dunedin this morning.