Tear Fund New Zealand says it is urging the Tongan government to formally ask for international help following Tropical Cyclone Ian before it is too late.
Its chief executive, Ian McInnes says the Tongan government wants to deal with the situation itself, with the resources it has and without requesting formal aid.
Mr McInnes says Tonga has a significant re-build programme ahead, with 500 homes destroyed, another 500 homes damaged, and infrastructure, roads and a wing of a hospital in need of repair.
He says Tonga has considerable public debt and it is not necessarily in an economic position to pay for these repairs itself.
"The fact is they have a very short but clear window of time to raise support for this, and then it will drop off the radar. The needs of the Tongan communities will be eclipsed soon enough in the media by other needs and other issues and the window will have passed. My view is that if they want significant international support, they should ask for that now."
Mr McInnes says Tear Fund and other aid agencies are responding anyway, through local staff on the ground.