Powerful cyclone brews in SW Pacific

A powerful tropical cyclone that could affect Fiji and Vanuatu is forming in the southwest Pacific Ocean.

The system was still a tropical low and was 1300km northwest of Nadi at 7am on Monday.

Fiji Meteorological Service acting director Aminiasi Tuidraki says the tropical depression, known as TD11F, is likely to reach cyclone strength by Tuesday.

He says the storm would not make a direct impact on the Fiji coast at this stage but the nation could expect rain, heavy at times, and strong, gusty winds by Friday.

Vanuatu Meteorological Services reports a moderate (40 to 60 per cent) chance the developing cyclone will move into its waters on Tuesday as it drifts south-southeast, rising to a moderate-to-high chance (40 to 70+ per cent) by Friday.

Bureau of Meteorology Queensland spokesman Jess Carey says the storm will not affect the Australian coast but could affect small Pacific nations.

"That's a really significant situation. That could potentially be a very large situation for Vanuatu and Fiji and all those southwest Pacific islands," he told AAP.

Mr Carey said conditions for cyclone development in the region are "quite favourable" and he expected the Fiji Meteorological Service would name the cyclone some time on Monday afternoon.