Insurance Australia Group and Suncorp's New Zealand divisions have cumulatively received over 8,000 claims so far following severe storms and flooding across the country.

As of Monday morning, Suncorp's Vero and AA Insurance brands have received about 3,000 claims, while IAG's AMI, State and New Zealand Insurance brands have obtained over 5,000 claims.

Both insurers expect the number of claims to rise further over the coming days, as the event continues to unfold and customers identify damages.

New Zealand's death toll from heavy rain rose to four on Sunday as flash floods and landslides on the North Island continued.

Battered since Friday, Auckland, New Zealand's largest city, remains under a state of emergency.

Thousands of properties remained without power, while hundreds were without water, NZ authorities had said.

Share price sinks on flood update

Both companies experienced a significant drop in their share price on Monday morning.

By 11:40am AEDT, shares of IAG had fallen 4.2% to $4.86, while Suncorp was down 3% to $12.42.

IAG noted that it was too early to determine the financial impact of the floods, and the company said it may review its $909 million estimate for fiscal year 2023 natural peril costs once the situation becomes clearer.

Suncorp said losses from this event will be capped at NZ$50 million ($45.7m) as its reinsurance program provides additional protection for New Zealand losses.

In a research note, brokers at Citi observed that IAG's exposure to the floods in Auckland (which could be potentially as much as $236 million) is "much greater" than the NZ$50 million cost Suncorp is likely to incur.

In comparison, IAG received 24,000 claims in the first three days of flooding in Sydney and across the New South Wales state last year.

Both insurance agencies, IAG and Suncorp, have a significant market in New Zealand.

Local New Zealand insurers have yet to provide any details on claims received.