With winds of up to 200 kilometres (125 miles) per hour, local disaster response officials said the cyclone had passed over the capital Port Vila before strengthening to a Category 4 storm.
There were no immediate reports of widespread damage or injuries, but the Vanuatu National Disaster Management Office issued a red alert and told residents to stay home.
Churches and official buildings have been earmarked as evacuation centres if needed.
The country's 320,000 residents are no strangers to powerful storms, but Judy is the strongest so far this cyclone season.
"The trees are down and any tree still standing is probably going to lose all its leaves and branches," said local UNICEF officer Rebecca Olul.
"It's gone through the whole of Vanuatu."
Related Links
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest
Subscribe Free To Our Daily Newsletters |
Subscribe Free To Our Daily Newsletters |