The Bay of Plenty's likely to see the worst of the strong deluge battering much of the country

It's been a rainy day for the top of the North and South Islands - with watches and warnings around Auckland and Waikato continuing into the evening.

The heavy downpour's already causing slips and major flooding - making driving conditions hazardous.

MetService metereologist John Law says the rain's falling hard in the Bay of Plenty, particularly eastern parts - and likely won't subside until early tomorrow morning.

He says rainfall totals could be as much as 230 millimetres in the ranges.