PORT VILA, Vanuatu — Relief workers rushed to deliver desperately needed food and water Wednesday to survivors living on Vanuatu’s outer islands, after a monstrous cyclone wiped out entire villages and flattened vast swathes of the South Pacific nation’s landscape.

Teams of aid workers and government officials were planning to send a boat packed with supplies to hard-hit Tanna Island, where aerial assessments showed more than 80 percent of homes or buildings had been partially or completely destroyed by Cyclone Pam.

Lack of food was a growing worry for those who survived the storm, which packed winds of 168 miles per hour when it struck Saturday.

“Everyone in Tanna and other islands in the south, they really live subsistence lives, so they grow what they need for a short period. … And the reality is that much of that would have been washed away by this storm,” said Tom Perry, spokesman for CARE Australia. “That’s a grave concern because we desperately need to get food to people soon.”

Flyover crews who surveyed the outer islands saw a flattened landscape and widespread destruction, with survivors below trying to signal them for help, said Colin Collett van Rooyen, Vanuatu director for aid group Oxfam.

Teams of aid workers and government officials carrying medical and sanitation supplies, water, food and shelter equipment finally managed to land on Tanna and neighboring Erromango Island on Tuesday, after being stymied in their efforts for days by poor weather and a breakdown in the nation’s communications networks. The two islands were directly in the path of the storm.

An aerial assessment showed extensive damage on Erromango, with communities ranging from 70 percent to 100 percent destroyed on the archipelago’s fourth-largest island. On other islands, Collett van Rooyen said plane crews saw people had made big, white “H” marks on the ground in multiple villages, and people on Tongoa island flashed mirrors to attract attention.

Radio and telephone communications with the outer islands were just beginning to be restored, but remained very patchy four days after Cyclone Pam tore through the island.

The U.N. Office for the Coordination of Humanitarian Affairs reported that 11 people were confirmed dead, including five on Tanna, lowering their earlier report of 24 casualties after realizing some of the victims had been counted more than once.