The Solomons has been afflicted by heavy rain and strong winds for the last two weeks, which have caused rivers to bust their banks and sweep through villages on the main islands of Malaita and Guadalcanal.
The flash flooding has contaminated drinking water and destroyed food gardens.
Director of the Disaster Management Office, Loti Yates, said food supplies and health and sanitation packs were needed as the risk of water and mosquito borne diseases was rising.
Eighty percent of those affected are subsistence farmers living in rural areas, Mr Yates said
But the flooding will also affect people living in the capital, Honiara, he said.
"The Guadalcanal plains is the food basket of Honiara," Mr Yates said.
"When you look at the amount of water running through, and it has been inundated for 5 or 6 days in most cases, you will know that root crops, vegetables and everything that usually gets trucked into Honiara markets will be very less now."
Photo Facebook Lowen Sei. Caption: Food gardens washed away during flooding in Tina River in Solomons