NUKU'ALOFA, Tonga — The most powerful cyclone in decades to lash the South Pacific nation of Tonga destroyed homes and ripped roofs from churches, killing at least one person, as authorities scrambled Sunday to assess damage.

Up to 70 percent of the homes and buildings in some areas had been flattened, said Kalolaine Kavaefiafi, spokeswoman for the child welfare charity Plan International.

Cyclone Ian hit Tonga on Saturday with gusts up to 287 kilometers (178 miles) per hour. The storm was later downgraded from the top of five-scale destructive cyclones to category four, with gusts of up to 250 kph (155 mph). On Sunday, the cyclone was tracking southeast away from Tonga.

An aerial survey of the damage was underway to assess the destruction and two navy patrol boats were on their way to the disaster area, Tonga's Director of Emergencies Leveni Aho said.

"It's pretty bad," Aho said of the damage. "By this evening, we'll have a much better picture of what's happened."

A state of emergency remained in effect for two of Tonga's three island groups, Vava'u and Ha'apai.

Aho said one person died on Lifuka island in the central Ha'apai group, where most of the islands had lost telephone contact. He did not know if the death toll was likely to rise.

Damage to homes and public buildings in Lifuka and Foa, the main islands in the Ha'apai group, was "quite substantial," he said.

The main island of Tongatapu in the south avoided the worst of the storm, with damage limited to some fallen trees, Aho said.

Authorities were still assessing how many people had been forced to seek shelter, he said.

Tonga is an archipelago of 176 islands, 36 of which are inhabited by more than 100,000 people. Its economy relies on fish export, tourism and remittances from Tongan communities overseas, with about 40 percent of the population living in poverty.