President Barack Obama speaks during a discussion about the importance of protecting the one planet. REUTERS/Yuri Gripas

WASHINGTON (Reuters) - President Barack Obama declared a state of emergency in Florida as Hurricane Matthew strengthened and headed for the U.S. Southeast, the White House said on Thursday.

The action authorizes the Department of Homeland Security and the Federal Emergency Management Agency to coordinate disaster relief efforts necessitated by the storm, a Category 4 hurricane packing winds of 140 mph (220 kph).