Whangārei floods
© Jesse Matthews
Local 4WD owners came to the rescue of a fire crew who were stranded in floodwaters in Whangārei last night.
A once-in-500-year storm has slammed Northland, flooding shops and forcing residents to evacuate homes.

Fire crews rushed out to 212 emergency callouts as the storm dumped 220mm on Whangārei.

The heavy falls caused slips and landslides that closed roads and limited water supplies.

Whangārei residents were this morning being asked to conserve water after the city's water treatment plants were "struggling to cope with the intense rainfall", Whangārei District Council said.

Residents in Onerahi and Whangārei Heads were advised not to drink or use tap water except in emergencies after a burst water main on Riverside Dr drained local supplies.

Flood waters were now receding and MetService had cancelled severe weather warnings for Northland.

However, the Far North remained "effectively cut off" by road closures from the severe flooding.

Meteorologist Alwyn Bakker said the intense storm had been created by the unusual interaction between two low-pressure zones in a manner that caused a direct hit on Northland.

"We've done some calculations over here in MetService," Bakker said of the storm.

"And 220mm for Whangārei has what we call a greater-than-500-year return period."

"What that means is we see this kind of thing once in every 500 years."

Bakker said MetService's continued thunderstorm watch meant rainfalls of 40mm-60mm an hour could still fall this morning.

By the afternoon, however, the storm should break and turn to periods of showers later in the day before petering off tomorrow.

Central Whangārei CBD was quiet this morning.

Western Hills Drive (SH1) was closed. Signs saying there is no access north of Kaikohe are along the road.

Across town, surface flooding and slips partially blocked Whangārei Heads Rd in a number of places. Traffic control was working in one section of the road as workmen cleared a large slip.