A fresh tropical cyclone has formed in the Pacific region and was gathering strength as it headed south towards New Caledonia and New Zealand, forecasters said Saturday.

A warning has gone out to all shipping in the path of Cyclone June to expect heavy swells and gale force winds.

June, which formed in the Coral Sea near the Solomon Islands as a category one cyclone, was expected to have intensified to category two before hitting Norfolk Island, between New Caledonia and New Zealand, on Sunday.

"Tropical Cyclone June is expected to produce a prolonged period of gale force winds, heavy rainfall and moderate to heavy swells over Norfolk Island on Sunday and Monday," Australia's Bureau of Meteorology said in a bulletin.

"Damaging winds averaging above 75 kilometres per hour (47 miles per hour) with gusts of about 100 kilometres per hour are expected to develop on Norfolk Island by about midday on Sunday."

Meanwhile, recovery operations continued in Tonga after Cyclone Ian slammed into the Pacific kingdom last week as a maximum category five storm and packing winds in excess of 200 kilometres per hour.

It left at least 4,000 people homeless and destroyed vital crops in the central Ha'apai islands.

The Tongan government said in a statement there was concern about the shortage of food and the supply of clean and safe drinking water.

The health inspector in charge of water and sanitation, Folau Hola, told Radio New Zealand the low-lying areas of Ha'apai were in a critical situation because of rising sea levels contaminating wells, and most rooftop collection systems were destroyed during the cyclone.