World Vision says Solomon Islands people in already damaged communities have been shaken by the latest big aftershock and many have fled to higher ground.
A 6.6-magnitude earthquake struck the Santa Cruz island group just before 6am on Friday (local time). It was 10km deep and located south-east of Kira Kira.
The tremor is one of the biggest of scores of aftershocks since Wednesday's 8.0 quake in the remote Temotu Province.
At least nine people have been killed after that quake triggered a one-metre-high wave surge that swept half a kilometre inland on the main island of the Santa Cruz group.
Friday's quake has not generated a tsunami warning and the Pacific Tsunami Warning Centre in Hawaii says there is unlikely to be one.
World Vision spokesperson Jared Berends, who is in the Solomons capital, Honiara, says teams are assessing the damage to villages from Wednesday's quake and tsunami.
Mr Berends says between 15 and 20 villages have been badly damaged.
A chartered plane was due to fly the Solomons Prime Minister, two doctors and supplies to Lata in Temotu Province on Friday morning.
Journalist Dorothy Wickham, based in Honiara, told Radio New Zealand's Morning Report programme the group will be confronted by scenes of devastation, as villagers' flimsy houses have been obliterated.
"They're mostly made of thatched leaf and local timber, so the damage would be total if there was a wave that went through - there wouldn't be anything left standing. It would be the same as what happened in Gizo in western province back in 2007.
"I think the most effects the community would be feeling now would be the lack of food, water and good shelter."
Ms Wickham said a patrol boat with food and medical supplies is due to arrive in Santa Cruz in the evening.