Category five is reserved for the most severe tropical cyclones.
Mr Waqaicelua said Tonga and the French territory of Wallis and Futuna would likely be hit with gale-force winds but would probably be spared the full force of the cyclone.
He said Fijians needed to take all precautions.
"It's our hope that no-one gets killed but the unfortunate can always happen in such disasters," Mr Waqaicelua said.
Fiji's self appointed prime minister Commodore Frank Bainimarama issued a statement urging every Fijian citizen to take the "impending disaster" seriously.
"I call on you to secure your homes, your businesses and your properties. I also urge you to now stock up on emergency and essential items. Every Fijian must be prepared and not be complacent."
People should restrict their movements and refrain from unnecessary travel.
"Because this is the festive season I ask you to consider cancelling social events and to act responsibly, all of us need a clear mind for what is bearing down on us. Alcohol and yaqona (kava) drinking will not help the situation," he said.
"Fellow Fijians, I cannot stress enough how serious this is."
In Samoa, the country's Red Cross secretary general Tala Mauala said makeshift emergency centres had been set up in churches, schools, sports clubs and government buildings to accommodate about 3000 refugees who had been forced to flee their homes.
People kept arriving at the centres, particularly from low-lying areas and communities near overflowing rivers.
"It's raining and getting cold, especially for the elderly and children. A lot of them said that all their stuff was taken by the floods, so they came up with what they were wearing at the time."
The Red Cross was giving out emergency supplies, harvesting rainwater, repairing sanitation and distributing lanterns to people who remained without power.
New Zealand's Foreign Minister Murray McCully said authorities in Samoa were coping "extremely well" with the situation and had not called on New Zealand for assistance, but help would be available at short notice if required.
None of the three dead were thought to be New Zealanders.
"The immediate issue is to ensure that we don't have a return of the cyclone and the picture at the moment is optimistic, though looking further out it's Tonga and Fiji that will be next in the firing line so we just have to ... keep our eyes on that potential."
Journalist Jonah Tui Le Tufuga told Radio New Zealand the damage in and around Apia was the worse than both cyclone Ofa in 1990, which killed seven people, and cyclone Val in 1991, which killed 16.
"It is phenomenal. I have experienced both Ofa and Val and I believe they have nothing compared to what Evan has done within 24 hours," he said.
"A lot of families are coming back to skeletons of their homes and most of their belongings being swept away when the river banks burst yesterday afternoon."
MetService weather forecaster Philippa Murdoch said the cyclone was not expected to have any impact on New Zealand at this stage.
* Cyclone Evan moves away from Samoa tonight and develops into a category four cyclone
* Brushes past Tonga and Wallace and Futuna Sunday morning, bringing gale-force winds
* Potentially develops into a category five hurricane as it hits Fiji with full-force on Sunday afternoon
- The United States is providing US$50,000 (NZ$60,000) to the Samoa Red Cross Society for immediate cyclone relief efforts, US Ambassador to New Zealand and Samoa David Huebner announced tonight (Friday).
"We remain in close contact with the Samoan Government as they continue assess their needs,'' he said.
Five- day forecast and animated satellite imagery from www.wunderground.com
- NZ Herald, APNZ, Newstalk ZB and additional reporting from Cherelle Jackson in Apia
