Relief groups struggled to get supplies to residents living in Vanuatu's cyclone-ravaged outer islands on Thursday, as survivors grew desperate for food and water five days after the fierce storm flattened villages across the South Pacific nation.

With power, phones and Internet still down across much of the country, officials faced logistical headaches in sorting out where to send supplies, particularly in Tanna Island, which was hit hard by Cyclone Pam's 168 mile per hour winds. Tanna's roads remained blocked by debris, forcing aid workers to hike across the island to inspect damage to schools and other buildings, UNICEF said.

"The phone network being down makes things incredibly difficult," said Evan Schuurman, a member of Save the Children's emergency response team. "It's meant that it's taken a lot longer to actually find out what's happening in some of the outlying islands, and so the sooner the communications can get back up and running, the better."

Though the death toll from the disaster stood at 11, officials and relief teams were growing increasingly concerned about islanders' long-term survival, with food and water scarce in the worst-hit areas and access to some of the archipelago's more remote islands remaining difficult.

More than 100 residents on Tanna, including the elderly and a newborn, have been sheltering in a store since Friday. With no relief supplies yet to reach them, they have taken to eating fruit they find on the ground and drinking water from a creek to survive.

Planes have been carrying food, water and medical supplies to Tanna and neighboring Erromango Island for two days, and a boat stocked with canned goods, biscuits and water was expected to head to the island on Thursday or Friday. But distributing it to the island's villages remains difficult.

"Food and water is the biggest issue in Vanuatu at the moment," Schuurman said. "So many people are subsistence farmers and entire crops have been lost."

UNICEF estimates that nearly 5,000 people across Vanuatu have no access to drinking water. The problem is especially worrisome on Tanna, which suffers from water shortages in the best of times.

Tanna's water towers were knocked over by the storm and wells built close to the shore were contaminated, said Sebastian Rhodes Stampa, disaster coordinator for the UN's humanitarian affairs office. Several more flights carrying water and water purification tablets were heading to the island on Thursday, and officials were hoping to set up water purification units, he said.

Around the capital, Port Vila, Save the Children workers spent Thursday distributing food and water to survivors sheltering in more than 20 evacuation centers.

"Most of them have lost everything — their homes have been badly damaged or some completely destroyed," Schuurman said. "A lot of them are from farming communities as well, and so they've lost their crops and they've lost their source of food, so this support is critical for survival."

Thousands of people remained homeless, with more than 3,300 sheltering in evacuation centers on Efate and in the provinces of Torba and Penama, according to the U.N.

Though officials were still conducting damage assessments and had yet to reach many of the outer islands, the nation appeared to have avoided mass casualties. Many locals rode out the cyclone in larger buildings such as schools and churches — a practice that relief groups have impressed upon Vanuatuans as a life-saving measure during storms.

Vanuatu is frequently battered by cyclones in the southern hemisphere's summer months and lies along the Pacific "Ring of Fire," where earthquakes and volcanic activities are common. Most communities have buildings designated as evacuation centers.

"A lot of people did evacuate," said Hanna Butler, an aid worker with the Red Cross in Vanuatu. "Here in the Pacific, we know that disasters happen every year at this time."