NAPLES, Fla. (AP) — Smoky conditions caused officials to shut down a section of Interstate 75 known as Alligator Alley on Thursday morning as four brush fires merged in southwest Florida, authorities said.

The four fires merged into a 4,000-acre (1,619 hectares) fire on Thursday, according to a tweet from the Florida Department of Agriculture & Consumer Services.

The Florida Highway Patrol said on Twitter that troopers were continuing to monitor conditions on Alligator Alley where the smoke caused visibility issues.

The agency advised motorists to proceed with caution and have set up detours. Nearby roads, including U.S. 41, remained open to traffic on Thursday morning.

Alligator Alley extends from near Naples on Florida's Gulf Coast, to Broward County in South Florida.

On Wednesday, officials said four fires were burning a total of about 400 acres (162 hectares), officials said on Wednesday night.

One of the fires threatened about 30 homes in the Collier County area of Golden Gate Estates, according to the Florida Forestry Service.

The Collier County Sheriff’s Office and the Florida Fish and Wildlife Conservation Commission were coordinating voluntary evacuations in the areas near the fires, the Naples Daily News reported.

The Greater Naples Fire Rescue District led efforts to fight the blazes, while two Lee County strike teams and one Sarasota County team also responded, Naples Fire Chief Kingman Schuldt said.