Vanuatu's Disaster Management Office hopes to have communication restored with its northern and southern provinces within 48 hours.
Authorities have struggled to contact the islands that bore the brunt of Cyclone Pam, which flattened buildings, smashed boats and washed away roads and bridges.
The official count of confirmed deaths is six with 30 people injured, however those numbers are almost certain to rise as rescuers reach outlying islands.
It has been three days since Cyclone Pam hit the Pacific archipelago.
The southern island of Tanna - about 200 kilometres south of the capital, Port Vila - and its 29,000 inhabitants took the full force of the category five storm.
The Red Cross has managed to reach the island and said it had been devastated.
One of the aid agency's specalists, Peter Lawther, arrived on Tanna yesterday.
He said it was flattened, with trees uprooted, no foliage, and no corrugated iron structures left on the western side of the island.
He said schools and concrete homes had also been destroyed.
National Disaster Management Office (NDMO) spokesman Mishael Lulu Garae said aircraft had been conducting reconnaisance missions over the provinces and were hoping to have a full assessment by tomorrow.
They also hoped cellphone coverage could be restored within two days.
Sune Gudnitz, the head of the United Nations Office for the Coordination of Humanitarian Affairs, said the first days after a natural disaster were critical.
"The long period of time without any contact with the southern islands of course is extremely worrying, because that seems to be unusual."
But Mr Gudnitz said unfortunately things could not have been done differently, as it was not possible to get out of Port Vila immediately after the cyclone hit.
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