More than 3000 people are without shelter in the quake and tsunami-hit Santa Cruz island group in Solomon Islands, as significant aftershocks continue.
The death toll has risen to 10 with the discovery of a child's body in a ditch near Lata airfield, with at least five more people missing.
The Solomons government has declared a state of disaster with officials saying damage on the main island, Ndende, is much worse than first thought, with up to 20 villages swamped in a tsunami generated by the quake.
The premier of Temotu province, Charles Brown Beu, says the number of homeless is expected to grow as rescuers reach more remote areas.
Father Brown Beu said people fled again to higher ground after a 6.7 tremor on Friday morning, the largest following Wednesday's 8.0-magnitude earthquake.
He says people need food and water, and most urgently, waterproof shelters.
The aftershocks meant a plane with supplies and medical staff couldn't land and was forced to return to Honiara.
Capital's residents camping out
Radio New Zealand International's correspondent says heavy rain is expected, increasing the urgency for shelter and fears of pneumonia for the vulnerable but at least providing some drinking water.
He says people from the provincial capital Lata are camping along the main road of the Santa Cruz plateau, possibly for up to a week until the situation calms down.
The hospital has been evacuated to an outdoor clinic with some patients having intravenous drips strung up in trees.
Red Cross relief workers with supplies are expected to arrive on a government patrol boat from Honiara on Friday night.
Red Cross secretary general general Joanne Zoleveke said there are widespread areas that no one has reached following the disaster.
"We're sending a 15-member team to Lata. We're relocating our operations centre there because we feel that the situation is grave and the devastation is more widely spread than we think it is."
She said only half of the main island in the Santa Cruz group has been covered so far and most of the outer islands remain isolated.
The Red Cross is also sending a water purification module and a sanitation unit on the boat.
Rise in volcanic activity
The Solomons National Disaster Management Office says volcanic activity has increased on an island in Temotu province since the biggest quake.
Sipuru Rove says the uninhabited island of Tinakula, which is about 50km north of Lata, has been making loud and strange sounds.
He says help and information is needed from technical experts to assess the risk posed to the local community by the volcano as they are worried an eruption could be near.
"The volcanic activity on one of the islands that is off Lata is alarming at the moment. And this will really require scientific special people to assist us in assessing this volcanic activity which is beginning to be abnormal."
A New Zealand volcanologist says it's very unlikely the quake will trigger a large eruption from the nearby volcano.
Dr Gill Jolly of GNS Science told Radio New Zealand International it has been proven that this can happen elsewhere in the world but only if the volcano is actively ready to erupt.
Dr Jolly said Tinakula is uninhabited and it is quite unlikely that its activity might impact on neighbouring islands.
She said a worst-case scenario would be a large eruption with the side of the volcano collapsing into the sea. causing another tsunami.
She said activity was being monitored before the quake but it looks like the main quake and aftershocks are predominantly related to the tectonic movements rather than the volcano.
Dr Jolly said New Zealand, Vanuatu and Solomon Islands governments hope to monitor active volcanos such as Tinakula more closely and build a Melanesian volcano network but this isn't yet fully established.