Sugar cane crops were destroyed as rivers burst their banks and hundreds of foreign tourists were stranded in resorts after flights were disrupted while roads and bridges were severed or submerged.
Authorities said at least six people have drowned and two others were killed in a landslide while more than 6,000 people have been forced into emergency government shelters.
Rajendra Prasad, director of Fiji's meteorological service, said two peak floods in succession was unprecedented and predicted that strong winds would accompany widespread flooding.
"This is the worst flooding situation in the recent history of Fiji," he told the Associated Press news agency, adding that with rivers bursting their banks he does not expect the waters to recede quickly.
On Monday the government declared a state of emergency in the hardest-hit western districts on the main island of Viti Levu.
Ratu Epeli, the defence and national security minister, had earlier told the Fijilive website that the curfews were "to safeguard lives and property", adding that dusk to dawn curfews were in place in several towns.
Patiliai Dobui , Fiji's disaster management chief, said initial damage estimates, excluding losses in the agriculture sector, ran up to $12m.
He said in towns like Ba on western Viti Levu, floodwaters more than three metres deep had surged through the area and submerged many homes up to their roofs.
"In Nadi, this is the worst flooding in the lifetime of most of the local people living there," Dobui told the AP.
Australia has announced it will give US$101,000 towards flood relief efforts in Fiji, adding to US$59,000 pledged by neighbouring New Zealand to the Fiji Red Cross.