Communities have been evacuated in remote parts of the Solomon Islands, with fears that many are without essentials.
The slow-moving storm - the strongest ever this far north in the Solomon Sea - has been battering islands for several days.
"These are very far flung places," Save The Children country director Tory Clawson told AAP.
"There have been no boats or flights in and out for four days, so there's a significant concern about food and water supplies."
The most destructive winds have been at sea, with the eye nestled between the two Melanesian nations.
Outlying islands have been hit hard: there are reports of three people missing at sea, food shortages, and destruction of homes and crops in the Western, Choiseul, and Isabel Provinces.
Solomon Islands Prime Minister Jeremiah Manele gave a national address on Thursday, urging fishers to remain off the water and for communities to rally around the most affected.
The region's biggest hospital, in Gizo, is in a state of emergency and only attending to emergency cases, according to the Solomon Star, with staff living in areas with damaged homes or at risk of landslides.
Storm surges have caused agricultural damage, while also contaminating drinking water.
Both are disastrous, especially given the high number of subsistence farmers, and the value of produce to trade at local markets.
Ms Clawson said establishing the full impacts and the scale of need would now be a priority.
"Many children and families have had to evacuate, often in the middle of the night," she said.
"As recently as last night, storm surges at 3am in the morning, meant a community had to flee to higher ground."
Mr Manele's government has committed an A$1.76m package towards immediate humanitarian needs.
Maila was a category five system on Wednesday, with peak gusts up to 295kmph, but as of Friday afternoon, was classed as a category three, moving west towards PNG's Milne Bay province.
Bureau of Meteorology tracking shows the storm will move across the region on Sunday as a category-two system, meaning the highest winds would be expected at 160kmph.
"From Sunday, Maila may track west southwest towards the Far North Queensland coast, possibly crossing Cape York Peninsula next week," a BOM spokesman said.
PNG's Woodlark Island, one of the biggest islands in the Solomon sea, is likely to be one of the hardest hit.
The cyclone's path will determine its strength if and when it reaches Australia, with some models suggesting a downgrade to a less destructive tropical low.
"Another possible scenario is for Maila to weaken near or over southeast Papua New Guinea over the weekend and not cross the Queensland coast as a tropical cyclone," the BOM said.
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