An Australian Defence Force (ADF) plane will head to Vanuatu within days to deliver relief supplies to the small Pacific nation after it was devastated by this week's Cyclone Harold.

Key points: Destruction in some parts of Vanuatu is worse than that caused by 2015's Cyclone Pam, aid groups say

Destruction in some parts of Vanuatu is worse than that caused by 2015's Cyclone Pam, aid groups say Authorities are concerned about the spread of COVID-19 as foreign aid arrives

Authorities are concerned about the spread of COVID-19 as foreign aid arrives Pacific nations' economies are heavily reliant on tourism, which coronavirus has devastated

The week-long storm has destroyed homes, cut off power and killed dozens in four Pacific island countries. Local disaster teams in Vanuatu hope to reach some of the worst-affected areas today.

Glen Craig from the Vanuatu Business Resilience Council estimates up to 90 per cent of homes in the country's second largest town, Luganville, have been damaged.

"It's worse than what we thought," he said.

"People here are positive. I think they're still a bit shell-shocked at the moment but they know that help is coming but help will need to come fast.

"Hopefully Australia and New Zealand military, especially, can start to mobilise — the airfield's fine for landing heavy aircraft."

Vanuatu authorities are concerned those bringing aid could introduce the country's first COVID-19 cases. ( Supplied: Australian Air Force )

Aid groups predict Vanuatu's recovery could take more than 12 months.

The ABC has been told the situation is "grim", with fears the damage in some places has been worse than Cyclone Pam, which hit Vanuatu in March 2015, killing at least 15 people and leaving the country with a damage bill of nearly $600 million — more than half of the country's annual GDP.

Kendra Gates Derousseau, the country director at World Vision in Vanuatu, told the ABC damage she had seen in Luganville and video of Pentecost Island, "indicate that the damage is significantly worse than tropical Cyclone Pam".

"The body of Harold was smaller than Pam, so the damage is less expansive in terms of numbers of islands, but the islands that were hit — it almost looked like a tornado had ripped through Luganville," she said.

"Instead of things being wind-blown and toppled, they were literally torn to pieces."

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The ADF will deliver relief supplies such as blankets, lanterns, shelter and hygiene kits. Defence Minister Linda Reynolds said the assistance for Vanuatu was "part of our commitment to stand shoulder to shoulder during times of crisis."

Foreign Minister Marise Payne said there would likely be more assistance announced in the coming days.

"We are acutely conscious that this comes on top of the impact and difficulties created by COVID-19 for those countries and so our support is all the more important," Senator Payne said.

New Zealand announced on Wednesday it would provide $480,000 to Vanuatu to help rebuild after the cyclone.

According to Vanuatu's National Disaster Management Office, however, "no foreign personnel are being brought to Vanuatu for response efforts at the present time".

"This will be an internally run operation," it said.

Any crew unloading supplies would wear protective gear and remain on the runway, authorities said.

The cyclone is the strongest to hit Vanuatu since Cyclone Pam in 2015. ( Japanese Meteorological Agency / Himawari-8 )

Tonga reels from Harold

The cyclone, with wind gusts of up to 285 kilometres per hour near its centre, severely damaged tourist resorts in Tonga yesterday.

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Local police reported three tourist resorts north of the capital, Nukualofa, had been virtually flattened.

Damage caused by Harold in Fiji, meanwhile, was worse than anticipated, the Red Cross told the ABC.

Prime Minister Frank Bainimarama said the country was "hit hard" but that he was "still waiting for the full damage report". Flooding caused by the cyclone continues to affect much of the country.

A tornado flipped the roof off a local college, Mr Bainimarama said in a message posted to Twitter.

"We've been through many cyclones before, even stronger than Harold. We always bounce back."

At least 27 people were killed in the Solomon Islands during the storm after they were swept off a ferry.

Australia has already provided support to the Solomon Islands and has offered assistance to Fiji and Tonga.

"We stand ready to provide further help to our Pacific family in whatever ways we can," Senator Payne said.

"It will be some time before the full impact of this disaster is known."

Fiji emergency management authorities are continuing to monitor flood-affected roads. ( Twitter: Fiji National Disaster Office )

Coronavirus fears complicate relief efforts

Pacific nations have implemented measures to prevent the spread of coronavirus, despite having relatively few reported cases.

While Vanuatu has not confirmed any cases of COVID-19, there are concerns the relief effort could compromise the vulnerable nation.

"Foreign-donated humanitarian supplies, which have initially come from our partners from Australia, New Zealand and France, are being handled to strict health protocols to negate any risk of COVID-19 coming to Vanuatu," a statement said.

Ms Gates Derousseau said Vanuatu had no intensive care beds and that if coronavirus hit, "it would have the potential to devastate the population".

The health systems in most Pacific countries were already struggling without a pandemic. ( WHO Western Pacific )

Pacific Islands Forum leaders on Wednesday agreed to establish a Pacific Humanitarian Pathway on COVID-19, which it said would allow for assistance to be expedited and distributed equitably among member countries.

Tuvalu Prime Minister Kausea Natano, chair of the Pacific Islands Forum, said coronavirus "poses a real and extreme danger to the health and security of the Pacific peoples".

"Never before has the full forum membership simultaneously been in crisis."

Cyclone Harold has caused significant damage across Vanuatu, Fiji, the Solomon Islands and Tonga. ( Supplied: World Vision )

The European Union, meanwhile, announced 119 million euros ($205 million) to assist Pacific nations to strengthen their health, water and sanitation systems in order to prevent the spread of coronavirus.

''The COVID-19 pandemic is the greatest global challenge of our time," EU ambassador for the Pacific, H.E. Sujiro Seam, said.

Fijian authorities have urged parents to keep their children indoors.

"Even though the cyclone has passed, the threat of floods is still present and we still need you to stay home because of COVID-19", a statement said.

Observers fear cyclone relief efforts will be further compounded by the economic consequences of COVID-19 social distancing measures.

Ms Gates Derousseau said tourism was 40 per cent of Vanuatu's budget, and was "unlikely to come back anytime soon".

Australian National University development economist Christopher Hoy told the ABC countries in the region such as Tonga and Samoa were already suffering from severe debt distress.