The Fiji Centre of Communicable Disease Control says four times as many dengue fever cases than usual in the past month may mean a new strain of dengue fever has reached the country.
A spokesperson, Dr Mike Kama, says from early November to mid-December this year there have been 42 reported cases of dengue, up for the normal 10 cases.
Dr Kama says there are concerns type-3 dengue has now reached Fiji, which has caused problems in other parts of the Pacific this year.
But he says there is a possibility the number of mosquitoes carrying type-1 dengue has increased, and the number of cases will die out once the population is controlled.
He says the centre has sent samples to a laboratory in Australia.
"If it's an introduction of a new strain, then this is very worrying for us. So we are trying to figure out what it is at the moment, and we are collating more data before we have a firm position on the situation that we have at hand."
Dr Mike Kama says the Health Ministry has issued a national advisory urging the public to take precautionary measures against the virus.