Fiji Meteorological Service - the agency responsible for Cyclone Donna - has confirmed the storm has spiked at Category 5.
That makes Donna the worst-ever tropical storm to hit the South Pacific in the month of May.
The record-breaking storm is still battering Vanuatu tonight before it is expected to head south toward New Caledonia. Meteorologists are still unclear on whether it will hit New Zealand.
Weatherwatch.co.nz said the Fijian weather agency's update would be of serious concern to those in Noumea and eastern New Caledonia.
In the north of Vanuatu, where the storm has been raging for days, numerous homes have been flattened and infrastructure has been destroyed, with many people at risk of disease from contaminated water sources.
Tonight the cyclone is battering Vanuatu's capital Port Vila with World Vision reporting evacuations due to flooding.
Residents are set to seek shelter in evacuation centres as the weather worsens.
Entire villages in the northern Torres group sought shelter in caves after the storm made landfall on Friday. Roofs were lifted and buildings destroyed as Donna carved a trail of destruction across islands in the Torba province.
Authorities were warning residents across central Vanuatu islands to find shelter.
Unicef spokesman Lachlan Forsyth told the Herald aid workers and the government were poised to help affected communities in the north, which have been weathering the cyclone for days.
"Part of the issue is that those communities are so incredibly remote and very hard to get in communication with. We are hearing from the Government that there are reports of housing being destroyed and damaged, schools being damaged," Forsyth said.
But the extent of the destruction was still unclear.
"It's very much a wait-and-see type of game."
World Vision staff in northern Vanuatu reported trees and power poles were down and water systems destroyed, with people forced to drink dirty water. Toilets had also been destroyed, increasing disease risk.
As of this morning, Donna had sustained winds of 215km/h gusting up to a ferocious 260km/h, making it the strongest May cyclone ever recorded in the Southern Hemisphere according to Weatherwatch.co.nz.
It eclipses Tropical Cyclone Nadu which struck in 1986.
New Caledonia is next in Donna's firing line as the vicious storm heads south. Donna is expected to track past Noumea early Wednesday morning.
Forecasters are still closely watching the cyclone's projected path across the Pacific with an update expected on Tuesday. They won't known until midweek when, or if, Donna will pose any major problems for New Zealand.
Even if it passes the country by it is likely to cause big swells and bring rain to parts of the country.
Donna would not be a tropical cyclone when it hit, but sub-tropical rain was likely. Dangerous beach conditions and gales were also possible.
MetService has said Donna poses no immediate risk to New Zealand.