Cyclone Rene is weakening rapidly as it moves toward the southwest of Tonga after causing havoc across much of the Pacific island group on Monday.
Rene is now classed as a Category 2 cyclone and at its centre has winds gusting up to 150km/h.
The Fiji Met Office warns that Ata, Tonga's most southern island, can expect damaging winds on Tuesday.
Tonga's Disaster Management Office has sent out teams to affected areas to assess the damage on the main island, Tongatapu, and outlying areas.
The cyclone had earlier damaged houses, knocked out power and flattened banana plantations in the Vava'u group, before battering Ha'api on Monday afternoon and hitting Tongatapu about 7pm.
Disaster officials say there was no loss of life or injuries, and most damage was to the power supply and the agricultural sector.
Tonga police Commander Chris Kelley says there was widespread damage to buildings and power lines in Tongatapu. Twenty-five families had to be evacuated.
Trees were blocking some of the roads on Tongatapu, the Defence Services said. Banana plantations and coconut and kassava crops have also been affected by the cyclone.
Radio New Zealand's Pacific Issues Correspondent reports the hospital has had no injured people brought to it.
Laura Jeffery, a resident of Ha'apai island group in the north of Tonga, where an estimated 8000 people live, says power and water have been cut. Plantations and homes have suffered minor damage.
NZ ready to help
New Zealand Prime Minister John Key says financial resources are available to help the Tongan government if it asks.
Mr Key says New Zealand was represented at the meeting organised by the Disaster Management Office in the capital Nuku'alofa on Tuesday.
A New Zealand Air Force Hercules has arrived in the Cook Islands with relief supplies and Defence Force personnel after Cyclone Pat hit the island of Aitutaki last week.
The Herclues can be diverted to Tonga if needed.
Aid agencies are also preparing to send staff to Tonga to help with the clean-up.