Flash flooding killed at least three people and left 10,000 homeless in the Solomon Islands' capital Honiara, with another 30 missing and the death toll expected to rise, aid workers said.

Entire communities were swept away as the city's main river, the Matanikau, burst its banks late Thursday, bringing down bridges and inundating the downtown area in a disaster observers said was one of the worst ever faced by the Pacific nation.

"The situation is quite dire," Save the Children's Solomons development program director Rudaba Khondker said on Friday.

"This level of rain has never been experienced before in Guadalcanal (the island where Honiara is located)."

Khondker said 16 evacuation centres had been set up in local schools to provide shelter for more than 10,000 homeless people, a huge proportion of the population in a city of only 70,000.

"It's a logistical challenge," she said, adding that roads had been cut and communications were patchy.

"The east side (of the city) is tough to reach and in the west side we're still carrying out assessments."

She said dengue fever, already common on the Solomons, was a major concern in the evacuation camps.

UN Office for the Coordination of Humanitarian Affairs' (OCHA) regional director Sune Gudnitz said the flooding followed days of heavy rain which was still falling.

"The water has not subsided and flood waters are continuing to build," he told AFP.

"The depression is threatening to turn into a category one cyclone in the coming hours and days."

Sourced from: weatherwatch.co.nz

Update:
There are now five people who have died in flooding in the Solomon Islands capital Honiara - and there are fears the death toll will rise as the weather worsens.