Tens of thousands of people in and around the Solomon Islands' capital Honiara have been left homeless by flash flooding and heavy rains.
Entire communities had been swept away, major access bridges had collapsed and roads had been destroyed with areas of the city isolated by the destruction, charity organisation Oxfam said.
As well as supplies, the Hercules would be also carrying emergency response staff from Government agencies and non-Government organisations.
Flooding last week claimed the lives of at least 21 people and thousands of people are in evacuations centres across Honiara.
New Zealand's initial $300,000 in emergency funding was going to World Vision and Oxfam which were distributing essential supplies there, he said.
"We will continue to work with the authorities in the Solomon Islands and further support will be considered as the full extent of the damage becomes clear," he said.
Unicef NZ director Dennis KcKinlay said an estimated 49,000 people had been affected by what was considered to be the worst flooding ever seen in the Solomon Islands, and 12,000 were staying in evacuation centres.
Unicef has people on the ground in the Solomons and he said the fact that the weather had cleared enough for assessments to be undertaken was a huge positive.
"Some shops are also up and running but they have only enough stockpiled to last a few weeks. Food security will be a huge concern in the coming weeks."
About 14,000 people and 14 communities had been affected by the flooding in Honiara, with 12,000 people seeking refuge in 16 evacuation centres set up around the region.
The number of dead is expected to rise, Oxfam's Solomon Islands' country director Katie Greenwood said.
Another 37,000 had been affected by the flooding in Guadalcanal province.
Oxfam was providing support to the Red Cross to manage the evacuation centres, which had been inundated with people, Ms Greenwood said.
"Around 20 per cent of Honiara's population are now in the evacuation centres, with 3500 in just one centre alone.
"We are facing enormous numbers here. The centres have been inundated with people who have lost their homes and their communities,'' she said.
Oxfam was also providing technical support and assistance, and remained on standby to help the National Disaster Management Office carry out disaster assessments of the region.
"We have relief items ready for distribution, and we are working to identify how we can support life saving efforts in the next stage of the government's response to this disaster,'' Ms Greenwood said.
By Rebecca Quilliam, Audrey Young