National Security Adviser Tom Bossert said at a news conference on Monday the federal government was focusing on emergency rescues, power outages and flooding in places like Jacksonville, where storm surge flooding has surpassed a record set by Hurricane Dora in 1964.

"Jacksonville and the Keys are taking a considerable amount of our attention right now," Mr Bossert said.

"If you are able, take care of strangers and others in need," he added.