SYDNEY: Fiji sent boats on Tuesday carrying desperately needed aid to remote islands and coastal villages devastated by a powerful cyclone which killed at least 29 people, as aid workers warned of possible outbreaks of Zika and Dengue viruses.

There are fears the death toll could rise in the nation of 900,000 people when communication resumes with the smaller islands hit by Cyclone Winston on Saturday.

Aerial footage of outlying islands taken by the Royal New Zealand Air Force, and posted on the Fiji government's official website, showed whole villages flattened and flooded after Winston's destructive winds, up to 325 kph (200 mph), tore through the archipelago of 300 islands. Thousands of Fijians live in tin or wooden shacks in low-lying coastal areas.

Authorities have warned of "catastrophic" damage to Koro Island, Fiji's seventh-largest island, and more than 8,000 people continue to shelter in evacuation centres across the country.

Prime Minister Frank Bainimarama reassured Fijians that the government was doing all it could amid growing criticism of the slow emergency response in some parts of the country.

"We realise the desperate position that you are in," Bainimarama said in a statement after visiting an evacuation centre. "We will not rest until we have reached you and given you the helping hand you so badly need and deserve."

"Unfortunately the recovery process will take time, perhaps a long time," he added. "Almost no part of our nation has been left unscarred."

Aid workers warned of potential outbreaks of the Zika and Dengue viruses, both carried by mosquitoes which will breed in the stagnant water left by the storm.

"The threat of dengue and Zika in the coming days in Fiji is real," said Chris Hagarty, senior health programme manager at Plan International Australia.

"The period immediately following a disaster of this scale can be a particularly dangerous one."

The World Health Organization declared a Zika outbreak in South America an international health emergency on Feb. 1, citing a "strongly suspected" relationship between Zika infection in pregnancy and microcephaly, a condition marked by unusually small heads that can result in developmental problems.

Much remains unknown about Zika, including whether the virus actually causes microcephaly. Brazil has confirmed more than 500 cases of microcephaly, and considers most of them related to Zika infections in mothers. Brazil is investigating more than 3,900 additional suspected cases of microcephaly.

Fiji's international airport at Nadi has reopened and an aeromedical evacuation team was being sent to outer islands on Tuesday to provide urgent support and supplies, including water and hygiene kits, medicines and access to shelter.