At least three homes were destroyed and hundreds of residents were under evacuation orders.
The largest fire was in Malabar, where about 3,000 acres burned and at least two homes have been destroyed. In nearby Palm Bay, another fire claimed one home and students at two schools were released early as a precaution.
About 80 miles north in Daytona Beach, an 800-acre fire forced an evacuation order for about 500 homes. No structures were reported damaged, though officials warned that embers could fly more than a mile from the blaze and spark new hot spots.
A Palm Bay firefighter was injured near Bayside High School, Palm Bay Fire Department spokeswoman Yvonne Martinez said. The name of the firefighter and the extent of the injuries were not known. A Daytona Beach firefighter was also treated at the scene for minor injures.
Hundreds of firefighters worked the blazes, bulldozing highly flammable brush and vegetation and leaving behind less flammable dirt to keep the fires from advancing. A Division of Forestry helicopter being used in Daytona was pulled off Monday afternoon and sent to help with the burgeoning Malabar blaze.
The state of emergency allows Florida to use federal funds and the National Guard. The declaration also brings local emergency workers under state control and allows Florida to call on other states for help, if necessary.
In Malabar, Butch Vanfleet, 59, tried to contain the massive fire with a garden hose before the flames engulfed his home.
Vanfleet said he built the house in 1980, and his 26-year-old son and wife were inside Sunday evening when the fire came to their doorstep. All that stood Monday was the chimney and a stone wall.
Vanfleet said he will rebuild.
"It's devastation," he said. "All you see is nothing but ash in between the palm trees and the palmetto. There's no grass. The fire just came so quickly, we barely got out of there."
The Florida Highway Patrol shut down a 7-mile stretch of Interstate 95 in Brevard County around rush hour Monday. U.S. Highway 1 was also closed in that area, and it was not known when it will reopen, FHP spokeswoman Kim Miller said.
"The fires have picked up in Malabar so it's just heavy, thick black smoke and it's right at driver level," Miller said.
Authorities said one person may be responsible for the Malabar fire. An eyewitness saw someone in a car drop something into an open field, and the fire started shortly afterward, said Ernie Dieble, an arson investigator with the Palm Bay Police Department.
In Daytona Beach, a 5-mile stretch of LPGA Boulevard was shut down because the fire was too close to the road. Investigators still aren't sure how the fire started.
Ray Ademski, a 68-year-old retiree, left his Daytona Beach home with his wife and their important papers when he saw columns of smoke Sunday night around the subdivision. He hosed down the roof and turned on the sprinklers in his yard before the couple left for a hotel.
"I could feel the heat from both sides," said Ademski, who returned by bicycle Monday to survey the damage. "The smoke was going straight into my eyes. It was terrible."
The fire was about 55 percent contained, but high winds and low humidity would continue to hamper efforts, said Timber Weller, a fire mitigation specialist for the Florida Division of Forestry.
"The risk of this fire breaking out is very high, so the crews are continuing to work very hard," Weller said. "By no means is this fire safe."
Firefighters also contained two smaller blazes near Cocoa that damaged four homes and two commercial structures, officials said.
In southwest Florida, authorities closed a stretch of State Road 776 near Charlotte County Sports Park because of a brush fire.
The LPGA Tour also closed its headquarters in Daytona Beach because of the fires.
