Florence approaches US, set to become 'extremely dangerous' storm

Hurricane Florence is expected to grow into an "extremely dangerous" hurricane by Monday as it approaches the US East Coast, the National Hurricane Center said, urging residents to make preparations.

"Florence is forecast to rapidly strengthen to a major hurricane by Monday, and is expected to remain an extremely dangerous major hurricane through Thursday," the NHC said in an advisory issued at 2100 GMT Sunday.

Forecasters said their hurricane hunter aircraft found Florence strengthening as it churned about 1,160 kilometres southeast of Bermuda.

The states of North and South Carolina and Virginia -- all potentially in Florence's crosshairs -- have already issued emergency declarations to help speed preparations.

"This storm is too powerful and its path is too uncertain to take any chances," South Carolina Governor Henry McMaster said in issuing his state's emergency declaration.

The US navy has ordered ships at its Hampton Roads, Virginia base to put to sea, saying "the forecasted destructive winds and tidal surge are too great to keep the ships in port."