Officials said six people were confirmed dead after Wednesday's quake generated a wave that swamped coastal communities on the island of Ndende in the eastern Solomons amid fears of a more widespread destructive tsunami.
Aid agency World Vision said some houses in the town of Venga were shifted 10 metres (33 feet) by the force of the surging water and almost all the homes in Nela village were washed away.
"I'm currently walking through one community and I'm knee-deep in water," World Vision emergency coordinator Jeremiah Tabua said. "I can see a number of houses that have been swept away by the surge."
The Solomon Islands Red Cross said the remoteness of the disaster zone, more than 600 kilometres (370 miles) from the capital Honiara, was hindering relief efforts, with the island's airstrip closed because of debris on the runway.
Red Cross disaster manager Cameron Vudi said reconnaissance flights would be made over the island Thursday to assess the scale of the damage but initial reports indicated at least 460 homes had been destroyed.
He said the death toll was likely to rise as reports came in from isolated communities.
"We're expecting changes. There are signs that there might be increases in the number of casualties," he told AFP.
"There are still reports coming in. Most of the reports are confined to areas that are accessible by road but there are a lot more communities that have been damaged."
The official death toll stands at six, with another four people missing, but a spokeswoman for World Vision Australia, who has been liaising with colleagues in the disaster zone, said it was believed at least eight people died.
National disaster management office spokesman Sipuru Rove said the Solomons government had asked the Royal Australian Air Force to send a plane to survey damage to the island.
"We're hoping for it to happen some time today, if possible," he told AFP.
Rove said an estimated 3,000 people were homeless, with many villagers fleeing the coast for higher ground and taking shelter in makeshift camps in the rugged hills.
Boats carrying medical teams and emergency supplies such as tarpaulins, fresh water, food and clothing were set to depart Honiara for Ndende on Thursday but are not expected to reach the stricken island until the weekend.
The US Geological Survey said the powerful quake struck at 0112 GMT Wednesday beneath the sea about 76 kilometres west of Lata, Ndende's main town, at a depth of 28.7 kilometres.
It was followed by dozens of strong aftershocks of up to 7.0 magnitude. The Hawaii-based Pacific Tsunami Warning Center put several island nations on alert for two-and-a-half hours before declaring the threat had passed.
In 2007 a tsunami following an 8.0-magnitude earthquake killed at least 52 people in the Solomons and left thousands homeless. The quake lifted an entire island and pushed out its shoreline by dozens of metres.
The Solomons are part of the "Ring of Fire", a zone of tectonic activity around the Pacific that is subject to frequent earthquakes and volcanic eruptions.
In December 2004, a 9.3-magnitude quake off Indonesia triggered a catastrophic tsunami that killed 226,000 people around the Indian Ocean.