Christian groups are at the fore of early relief efforts as Hurricane Matthew, the most powerful hurricane to hit the United States in a decade, brings storm surges and lashings of rain to Florida after killing at least 339 people in Haiti.

Southern Baptist Disaster Relief leaders in Florida, Georgia and the Carolinas and the North American Mission Board (NAMB), which reported the Christian relief effort on its website, are aiming to help in any way they can.

Southern Baptists have 65,000 trained volunteers and 1,550 mobile units for feeding, chainsaw, mud clearance, child care, power supplies and other essential services.

"We've been in close contact with our state partners and are preparing to help in any way we can," said Mickey Caison, one of the team. "The potential for harm to people and massive property damage is certainly a major concern. We began our first Matthew planning meeting, as we do all of our state partner meetings, in prayer."

The Christian relief workers are in talks with the American Red Cross to ensure the best way of helping. Ensuring clean water, food, clean-up and then recovery are their priorities.

President Obama has declared states of emergency in Florida, South Carolina and Georgia and million of people have left voluntarily or been evacuated from the three states.

The hurricane is "as serious as it gets", the President tweeted.

The Billy Graham Rapid Response units also have teams ready to move in and help, all while continuing their response to south Louisiana flooding and other disasters.

And today, Christian Aid launched an appeal, saying: "Hurricane Matthew has swept through Haiti, leaving a trail of devastation in its wake. Thousands have lost their homes, corn and banana crops have been flattened, and livestock have been swept away. The death toll is rising as emergency workers slowly start to gain access to remote areas that have been cut off by the storm.

"We've been working in Haiti for nearly 20 years. Our partners helped evacuate people to shelters as Hurricane Matthew approached, and made sure that the shelters were stocked with food over the weekend. Now they're assessing the damage the storm has caused and working out how best to help people.

"Please give whatever you can today to our Hurricane Matthew Appeal so that our partners can support communities to get back on their feet sooner rather than later."

National Hurricane Centre said the hurricane was bringing winds of 100 miles per hour and potential storm surges of up to 10 feet as heavy rain hit Florida, leaving 300,000 homes without power.

Daytona Beach Mayor Derrick Henry told CNN: "We are just bracing and the winds are picking up. A great number of our residents have taken heed to our warnings and we are certainly concerned about those that have not.".

Hundreds of passenger flights were canceled in south Florida, and cancellations were expected to spread north in coming days along the storm's path.

Also in Florida, fuel stations on Thursday afternoon posted "out of gas" signs after cars waited in long lines to fill up. At a Subco gas station in Orlando, the pumps had run dry on Wednesday.

The shop was a stopping point for coastal residents seeking shelter inland. Among them was Jonas Sylvan, 44, of Melbourne, Florida, who planned to hole up in a hotel with his wife, two daughters and dog. "We're just trying to get away from the coast," he said. "It's safer here."

Additional reporting by Reuters