The North Island and the upper part of the South Island are enjoying the warmest conditions on Boxing day, with many heading to nearby beaches and rivers.

Temperatures are into the 20s already in these areas with those in sheltered and sunny areas expecting the thermometer to go even higher this afternoon.

Cloud and some rain or showers are moving up the lower parts of the mainland with cooler conditions but a sunny day is expected for most in the south tomorrow with temperatures on the climb.