Hurricane Matthew has killed at least 14 people as it battered the US east coast.
As the storm hit there were major floods and power outages in Florida, Georgia, and North and South Carolina.
Matthew - which was a category 5 storm when it hit Haiti last week killing nearly 900 people - has since been downgraded to a post-tropical cyclone but at one point hit wind speeds of over 157mph.
Britain will give up to £5 million of initial aid to the victims of Hurricane Matthew in Haiti, including temporary shelters, water purification kits and solar lights, to battle the heightened risk of epidemics such as cholera.
The aid will target 12,500 of the most vulnerable people as experts from the Department for International Development (DfID) continue to help UN and NGO partners address the impoverished Caribbean nation's most pressing needs.
International development secretary Priti Patel said Britain would "play its part" by providing expertise and support to help those caught up in the aftermath of the "worst storm to hit this region in almost a decade".
"The absolute priority right now is to reach those who are injured and provide them with water, sanitation, shelter and protection," Ms Patel said.
Matthew - which was a category 5 storm when it hit Haiti last week killing nearly 900 people - made landfall in the States on Friday.
As Hurricane Matthew approaches Florida, its 140-mile-an-hour winds have already left behind a trail of destruction in Haiti.
Residents told to fully prepare for the arrival of the hurricane with warnings its impact could be "devastating".