WELLINGTON, NEW ZEALAND -- A dangerous amount of rain is forecast Tuesday for New Zealand's most populous city four days after Auckland had its wettest day on record in a storm that claimed four lives.

A state of emergency was declared on Friday when a volume of rain that would typically fall over an entire Southern Hemisphere summer hit in a single day. At least 5,000 homes and businesses were being assessed for flood and landslide damage and several roads remained closed after more than 15 centimetres (6 inches) of rain fell in three hours.

The state of emergency for Auckland and surrounding districts was lifted on Monday morning. But Auckland Mayor Wayne Brown warned that dangerous conditions were forecast to return on Tuesday.

"My team's current focus and our big worry is that some Aucklanders might think the worse is behind us, but it isn't," Brown told reporters.

Brown said up to 12 centimetres (almost 5 inches) of rain was forecast in some areas that were already waterlogged.

"That's nothing like Friday night, but the ground is so saturated and the drains are so full that if anything, it could be more dangerous than even Friday," Brown said.

Brown said the number of residents of Auckland and surrounding areas asking for help due to storm damage would continue to rise.

"It has taken some time for everyone to appreciate just how big and widespread an event this has been and it hasn't finished yet," Brown said.

"The downfall was by far the biggest in our history. It was well beyond even what our emergency people either imagined or planned for," Brown added.

The heavy rain warning for Tuesday covered Auckland and further north on the North Island.

"This rain is expected to cause dangerous river conditions and significant flooding. Slips and floodwaters are likely to disrupt travel, making some roads impassable and possibly isolating communities," a MetService statement said.

Auckland schools will remain closed until next week.

Auckland Airport has resumed operations that were shut down by the storm Friday, but the airport warned in a statement that flight schedules may be disrupted for several days.