Moroivalu adds they are closely "monitoring the situation" and will seek help from the "Fiji Military Forces and the police" if the situation deteriorates.
Schools directly in the path of Cyclone Gita have been ordered to shut down and parents have been advised to keep their children at home for their safety.
All schools on the islands have further been advised to fasten all "loose structures, trim overhanging tree branches and fill and secure water tanks.
The Education Ministry is pleading with families to stock up on emergency supplies and place shutters over windows and doors as Cyclone Gita intensifies over the day.
With heavy rain forecast, the weather office in Fiji has warned of flooding in low-lying areas and advised coastal communities and those close to rivers to take all necessary precautions.
Fiji Red Cross secretary general Filipe Nainoca said they would likely be unable to travel to the island group from the main island Viti Levu until Thursday or even Friday.
"We expect the islands to be inaccessible today and tomorrow," he told the Herald.
"They are closer to Tonga than they are to Viti Levu.
"On Thursday we might be able to do air surveillance, but we will have to wait for the waves to settle before we can get there by boat."
There were about 400 people living on both Oni-i-Lau and Vatoa, the islands likely to be hit the hardest.
"The main problem is they are low-lying attols and will be greatly affected by storm surges. There could be issues with shelter and water supplies becoming contaminated with sea water. That was a major problem in similar islands during Cyclone Winston.
"Winston was a category 5, and this is category 4. We hope it stays that way, or even goes lower.
"Everyone in Fiji is watching, and is very concerned."
The evacuation centres were in schools and halls, and other areas on high ground.
"They are already feeling the winds there now. A big problem is the cyclone is moving slowly, meaning the strong winds could hang around there all day tomorrow."
Fiji Red Cross was preparing supplies and volunteers to head over to assist as soon as the cyclone had passed.
After Cyclone Gita hits Fiji it will track over open water towards New Caledonia and Norfolk Island. It still forecast to grow into a category 5 cyclone.
WeatherWatch has predicted that Cyclone Gita is likely to swing out into the Tasman Sea then curve back around a make a direct hit into New Zealand. However it is not known whether it will retain its storm conditions. It could make landfall in New Zealand any time from this Sunday to next Wednesday.