The chairman of the Ba Mission Hospital has confirmed two people died in the town, and two others are in a serious but stable condition.
Fiji media report five other deaths, including two in Ovalau island, one from Koro Island, one from Tailevu and one from Ra province, in the north of Viti Levu.
The category five Cyclone Winston has been described as the strongest storm ever recorded in the Southern Hemisphere.
Winston tore through the Fijian mainland and neighbouring smaller islands, bringing wind gusts of up to 325kmh.
Jay Dayal said every street in Ba had fallen power poles and trees following the storm, which were preventing access in and out of the other medical centres where there could be other serious cases.
Power had been restored at the hospital with a backup generator but there was no word on when the roads will be cleared.
Mr Dayal said 20 injured people had been treated and discharged and the two seriously injured were under observation.
"They are stable though, but they have got cuts on their face and their body. They have been hit by flying objects and they are in a stable condition now."
Jay Dayal says the destruction is the worst he has ever seen and the town is unrecognisable.
Hundreds of people have fled to evacuation centres. A curfew remains in force as the authorities go about assessing the damage.
All schools in Fiji will be closed for a week as they work to deal with the aftermath of the storm.
Winston is now heading west away from Fiji but is still a category 5 storm.
Some Fijian families were trapped under collapsed roofs, ceilings and walls while the cyclone was at its peak.
Disaster officials said many houses have been badly damaged in Rakiraki, Tavua, Ba, Lautoka, Savusavu, Lau, Taveuni and Nausori.
UNICEF worker Alice Clements said some homes in the worst affected areas look as though they have been stamped flat.
'There's not one house that has not been damaged'
Earlier Jay Dayal RNZ News every single house in the town of Ba was damaged and there were whole suburbs wiped out.
"There's not one house that has not been damaged. Every house has sustained some damage. Some of the houses have just falled flat. Some houses with no roof at all. Total devastation. We see power lines all over the place, power lines have fallen, big trees have fallen."
Jay Dayal said there was a fear of flooding due to the heavy rainfall in the town and on the nearby mountains.
The roof of Pritesh Sahay's home in Tavua was blown off, and she said many other homes in the northern town suffered similar damage.
"Power lines are down, fallen power poles, trees have fallen, cars have been damaged," she said.
"People are saddened because their hard work has been wasted but they're still managing to clean up their compounds as the rain still continues."
Warren Francis runs a safari lodge on a small Island, north of the main island Viti Levu - one of the worst affected areas. He said the cyclone felt like a freight train was hitting the lodge.
"You get the courage to peer out through the glass and see an incredible amount of swing in a coconut tree, then branches go past the windows and not just small ones," he said.
He said the island was like a bombsite, with soil stripped from the ground, trees snapped like matchsticks, and a 15-foot wide water tank from a kilometre away smashed on his property.
Sulueti Waqa, who lives near the town of Ba, in Viti Levu, said she estimated 90 percent of her settlement had been destroyed. The cyclone had also ripped the roof off the hospital, houses were flooded and crops wiped out.
Fiji Education Minister Mahendra Reddy said some schools would have been completely devastated, and all schools were to remain shut for one week to allow for the cleanup.
A curfew was in force as the authorities began to assess the damage. A briefing was to be held at midday New Zealand time in Viti Levu, Fiji's main island.
Relief efforts underway
MetService said it was the strongest tropical cyclone to ever hit the country.
New Zealand has sent an Air Force Orion to Fiji to help survey cyclone damage.
Aid agencies said they were well-prepared, and would take the lead from the Fijian government, which was sending out rapid assessment teams today.
Ian McInnes is the chairman of the Council for International Development, which represents 18 aid agencies, including Unicef, Tearfund and Oxfam. He said the storm would likely have a devastating impact on agricultural production and food supply.
"I think what we'll see today is agencies make a calculated decision about whether they'll launch a full-blown appeal," he said.
"A lot of agencies are taking funds now, they all prepare ahead of time in case of disasters in the Pacific."
The Pacific regional director for Oxfam, Raijele Nicole, said the aid charity was still discussing how it could help Fiji's government.
"We've got staff throughout the Pacific and in Australia and New Zealand. The most important thing is to share information and work together to co-ordinate a response with the other NGO's so we can meet the needs of the government," she said.
Officials said the Urate village of Savusavu was badly damaged in the storm.
Fijian radio reported 133 people stranded in Savusavu town were evacuated to the nearby Yaroi village hall
Roads were washed out, making it difficult for authorities to travel around the village, with some roads blocked by rocks.
A bus was also washed inland by a strong tidal wave.
Large parts of Fiji were without power, and people were told to stay indoors until power lines and fallen trees were cleared.