It's a double whammy of heading towards summer this weekend as the astronomical end to winter arrives, marking the spring equinox - as well as daylight saving beginning.

The spring equinox occurs at precisely 6:49pm on Saturday this year in New Zealand, says WeatherWatch.co.nz

"The equinox means the Northern Hemisphere and Southern Hemisphere have equal length nights and days at the moment ... and in the weeks ahead the days in the Southern Hemisphere will become longer than the nights.

"Then, several hours after the equinox, in the early hours of Sunday morning - the last Sunday of September - we spring forward one hour at 2am to start Daylight Saving. So 2am Sunday NZST becomes 3am Sunday NZDT.

"We'll have more details on the spring equinox, daylight saving plus the current ultra-violet (UV) rays across NZ, the South Pacific and Australia as we head closer towards summer."

Earth's equator lines up directly facing the sun meaning the Northern Hemisphere and Southern Hemisphere have equal length days and nights, says the weather organisation.

"In the coming weeks the earth tilts further to make the Southern Hemisphere more directly face the sun, creating longer days (more hours of sunlight/shorter hours of darkness) up until late December in the Southern Hemisphere - and bringing longer days for the next six months.

"It also means the start of Autumn and shorter days/longer nights for our Northern Hemisphere neighbours."