Cyclone Heta has hit the tiny South Pacific island of Niue, wreaking widespread damage with winds of up to 300km/h (185mph), local sources said.
Heta has been moving south across the Pacific
The capital, Alofi, has been flattened, with at least one person dead, according to a New Zealand diplomat.
A state of emergency has been declared on the island, which has a population of 2,100.
"I'm absolutely worried for my little country," said Premier Young Vivian, who is presently visiting New Zealand.
Mr Vivian had left Niue to attend his wife's funeral, and he is now stranded in Auckland, unable to return home.
All normal communications with Niue have broken down, although the New Zealand foreign ministry managed to contact its high commissioner by satellite phone.
She reported widespread damage to crops and buildings.
Twenty New Zealanders who were on holiday on Niue have been accounted for.
New Zealand is planning to send an aid flight as soon as possible to Niue, which lies about 2,700km (1,675 miles) north-east of the capital, Wellington.
The plane will contain emergency equipment, and a team will carry a full assessment of aid needs.
The island's only hospital is reported to have been damaged.
Premier Vivian said that the country's cash crops - taro, vanilla and limes - had probably been destroyed.
"Any cyclone with that strength, that force, is going to
wipe out whatever efforts we have made in the past years in
terms of agricultural products," he said.
More Niueans live in New Zealand than in their own country, because of unemployment.
A tiny coral atoll, Niue would have had no protection against the force of Cyclone Heta, which had reached a strength of category five, the highest cyclone rating.
It had already hit American and Western Samoa, Tokelau and the northern islands of Tonga.
Samoa suffered damage to crops, roads and buildings, but reported no serious casualties.
Cyclone Heta is now reported to be 500km (310 miles) south-east of Niue, and weakening.