Fiji. Image Credit: Reuters

Suva: Fiji and Tonga issued severe weather warnings Tuesday as twin cyclones intensified near the Pacific island nations.

The Tonga Metservice said Tropical Cyclone Zazu was a category one system, currently packing winds of up to 90 kilometres an hour (56 miles an hour), and expected to reach category two on Wednesday.

Meanwhile, forecasters in Fiji said Tropical Cyclone Yasa had reached category three status as it rumbled off the coast of the main island Viti Levu, and could turn into a category five super-storm late Thursday.

Authorities in both countries advised residents to prepare for strong winds and flash floods, with Fiji's Disaster Management Office flagging possible evacuations later in the week.

The New Zealand-based meteorological service Weatherwatch said the twin cyclones were unlikely to join up but their proximity to one another did complicate forecasting.

"It makes it a little tricky to know exactly how close Yasa will get to Fiji - direct hit is the current thinking," Weatherwatch managing director Philip Duncan said.

The storms are the first to form in the South Pacific's current cyclone system, which runs until May next year.

The region was battered by Tropical Cyclone Harold in April this year, a category five storm that gouged a trail of destruction across the Solomon Islands, Vanuatu, Fiji and Tonga.

Such top-of-the-scale cyclones were once rare but have become increasingly common in recent years, with Fiji's Prime Minister Frank Bainimarama among those blaming the phenomenon on climate change.