Krome Avenue was closed again between Okeechobee Road and Tamiami Trail Thursday afternoon because of smoke from wildfires that were started by lightning a day earlier.
The road, which was shut down overnight and reopened in the morning, could remain closed for hours, officials said.
The largest of the fires - at 400 acres long Wednesday night -- had spread to 1,000 acres midday Thursday. It was not threatening any homes, and no one had been evacuated.
''This is undeveloped land,'' said Lt. Eric Baum of Miami-Dade Fire-Rescue. ``You don't have threats to people or structures.''
Lightning storms with no rain sparked three fires in west Miami-Dade in the Everglades between 4 p.m. and 5 p.m. Wednesday. The fires spread smoke over much of Miami-Dade County -- Fire Rescue received reports of smoke from as far as Miami Beach.
''With the humidity, the smoke rises and sort of stalls,'' said Baum. ``We are telling residents who are experiencing breathing problems to turn on their air conditioners and shut the windows.''
Susanne Etheridge, duty officer at the Florida Division of Forestry, said residents should expect the smoky conditions to continue.
''It depends on how long the fire burns,'' said Etheridge. ``The smoke will stop whenever they burn themselves out.''
She said firefighters are having a tough time containing the fires because the ground is too soft and the grass is too dry.
''They just have to let it burn,'' she said. ``We are monitoring it and making sure it doesn't come close to any property.''