Auckland Emergency Management has issued an alert to mobile phones warning that an active line of thunderstorms poses the risk of "very high intensity, localised downpours".
The emergency alert told people to stay informed and to keep up to date with the latest information.
It also advised people to head to higher ground if they saw rising water, instead of waiting for official announcements.
MetService has issued a severe thunderstorm watch for Northland and Auckland until 10am tomorrow and a heavy rain warning is also in place for both regions.
Further south, a thunderstorm watch is in place for Whanganui, Manawatu, Tararua, Kapiti-Horowhenua, Wairarapa, and Wellington through to 9pm this evening.
MetService said the thunderstorms could become severe, producing localised downpours of 25-40mm per hour and possibly large hail.
Up to 40mm/h of rain was possible in pockets of Tāmaki Makaurau and Northland, though it was not expected to be as extreme as Friday's weather event.
Auckland Emergency Management said it had particular concerns for areas north of Orewa, where slips may occur.
Meanwhile, the death toll from this week's flooding around Auckland has risen to four, after the body of a man swept away by floodwaters in Onewhero on Friday was found.
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