The Solomon Islands Meteorological Service says tropical cyclone Sandra has been upgraded to a category three system.
A tropical cyclone warning is in force for Rennell, Bellona, Southern Guadalcanal, Makira islands and Temotu Province.
A tropical cyclone watch advice is also current for the remaining provinces and islands.
The system is moving east-southeast at 6 kilometres an hour and intensifying.
The meteorological service says there is potential of sea coastal flooding and flooding of low lying areas.