WELLINGTON - New Zealand is sending an air force Hercules with relief supplies to the flood-ravaged Solomon Islands.

A state of emergency was declared after Honiara's main river, the Matanikau, burst its banks late on Thursday, sweeping away entire communities and destroying infrastructure.

"A RNZAF C-130 Hercules will depart from New Zealand tomorrow morning carrying relief supplies, and emergency response staff from New Zealand government agencies and non-government organizations," New Zealand Foreign Minister Murray McCully said in a statement on Sunday.

There are now 21 confirmed deaths and significant numbers of displaced persons in evacuation centers across Honiara.

"New Zealand police on deployment as part of the Regional Assistance Mission to the Solomon Island (RAMSI) are already assisting with the response in Honiara," he said.

New Zealand's initial 300,000 NZ dollars ($255,000) in emergency funding has been provided to World Vision and Oxfam who are distributing essential supplies.