The South Pacific nation of Tonga was lashed by a powerful cyclone on Saturday, destroying homes and ripping roofs from churches and other public buildings in the populous northern islands. There were no immediate reports of injuries.

A state of emergency was declared for two of Tonga's three island groups, Vava'u and Ha'apai,  on Saturday morning as category-five storm Cyclone Ian brought heavy rain and strong winds forecast to gust at up to 287 kilometers (178 miles) per hour.

The storm was later downgraded from the top of the scale of destructive cyclones to category four, with gusts of up to 250 kph (155 mph).

The main island of Tongatapu in the south appears to have avoided the worst of the storm.

Tonga's  Director of Emergencies Leveni Aho said damage to homes, churches and other public buildings was reported on Lifuka island in the central Ha'apai group and Hunga island in the Vava'u group to the north.

The extent of the damage was still being assessed, but the destruction appeared to be less extensive than Tongans had feared from the first category-five storm they had experienced in decades.

"The lucky part ... is that although it is very highly dangerous, the eye was so narrow, the extent of the damage is not what you associate normally with a category-five cyclone," Aho said. He estimated the storm's eye was less than 60 kms (35 miles) across.

He said there were no immediate reports of deaths, injuries or missing persons.

While churches had been prepared as standby evacuation centers, Aho said he was not aware of people leaving their homes in large numbers.

Aho advised against travel between Tongan islands during the storm and urged residents of outer islands to stay put.

Tonga is an archipelago of 176 islands, 36 of which are inhabited by more than 100,000 people.(AP)