Low-lying areas in the Ha'apai island group suffered the worst damage in Tonga from Cyclone Wilma, the National Disaster Centre says.
The Category 3 cyclone hit on Tuesday morning, causing damage to many houses and roofs and caused some village town halls to collapse.
The Ministry of Tourism says businesses are beginning to clean up after winds of up to 166km/h combined with a high tide.
Food crops throughout the island group have been devastated and many buildings damaged. Ha'apai resorts have reported damage to waterpipes and flooding, with some beach bungalows washed offshore.
The ministry's director, Akopo Lolohea, says some tourists are stranded in resorts, but things are now returning to normal.
On the islands surveyed so far, the Ha'apai governor's residence suffered extensive damage, an office at the airport was demolished, several church structures were badly damaged and some schools suffered damage, Radio New Zealand International reports.
The acting secretary for the Ha'apai governor, Viliami Taumoefolau Latu, says low-lying areas including Lifuka experienced severe flooding, with storm surges reaching up to 20 metres inland in places.
Power is still off in places due to many electricity lines being blown down.
National Disaster Centre spokesperson Mafua Maka says about 10 new houses have been affected, much of the roof of a school building was torn off and breadfruit, banana and fruit crops have been severely damaged.
Mr Maka says other areas, including Vava'u and the main island of Tongatapu are reported to have suffered less damage.