The deadly tsunami that struck the Solomon Islands on Monday damaged hundreds of homes, many of them on Gizo island.
People fled to high ground when the waves struck and many remain in hill camps. There are fears diseases could spread.
Many are afraid to return to seafront homes for fear of aftershocks.
Munda island was also badly affected when the 8.1 magnitude quake struck.
Aid has been slow to reach some of the islands because of their remoteness.
The UN said although there were warnings, there was little time in some areas to react.
About 30 people are thought to have died but the full scale of the disaster is not yet known.