Hurricane Matthew wreaked havoc in parts of United states. The storm, which is blamed for four deaths in Florida, sparked flash-flood concerns. The National Weather Service issued a warning for parts of Nassau County, north of Jacksonville. It killed more than 800 people and left tens of thousands homeless in Haiti earlier this week before it skirted Florida's Atlantic coast on Friday and plowed northward over waters just off Georgia. US President Barack Obama urged people not to be complacent and to heed safety instructions. "The potential for storm surge, loss of life and severe property damage exists," Obama told reporters, after a briefing with emergency management officials about the fiercest cyclone to affect the United States since Superstorm Sandy four years ago. Hurricane Matthew has left more than 1 million people without power. Officials Georgia and South Carolina urged coastal residents to head inland as the most powerful Atlantic storm in more than a decade continued on its path along the coast.