(CNN) -- After the crashes stopped, Steven Camps said, all he could hear was the sound of crying as the air, heavy with smoke, shone red from vehicle fires.
He pulled his friend from their car, which wound up wedged between two tractor-trailers. The two were lying in the grassy median of Interstate 75, he said, praying that a car would not leave the roadway and hit them.
The vehicle Camps was riding in was among those involved in a series of overnight accidents in northern Florida, blamed on poor visibility from smoke from a nearby brush fire, authorities said. Ten people were killed in the crashes, which the Florida Highway Patrol said involved at least 12 passenger cars and about seven semis.
Most of the collisions were on Interstate 75, said Alachua County Sheriff's Office Sgt. Todd Kelly. Crashes also occurred on U.S. Highway 441.
The interstate's northbound lanes reopened, but southbound lanes remained closed Sunday evening, the Florida Highway Patrol said. Traffic was being detoured.
Late Sunday, the National Weather Service in Jacksonville issued a dense smoke advisory for early Monday morning. Smoke from nearby fires will cut visibility to less than a mile in some places, it said. While the dense smoke advisory expired at 8 a.m. ET, the weather service said later Monday that patchy smoke was possible and warned of reduced visibility.
"We will monitor the roadways and be prepared to take action," said Florida Highway Patrol Lt. Patrick Riordan.
The fire responsible for the smoke, called the Boardwalk Fire, was 100% contained but was not considered controlled, Ludie Bond, wildfire mitigation specialist for the Gainesville area, said Monday. While fire lines were in place, active smoke could linger for weeks to months, she said.
Camps said he was returning to Gainesville from Micanopy, about 12 miles away, with a friend early Sunday on I-75 northbound when traffic came to a stop on the interstate in what looked like heavy fog.
"It was just so crazy," he said. "We were just sitting in the car, and all of this came out of nowhere."
Camps, a passenger in the car, said they were talking to a man in a stopped car in the next lane about the low visibility when they began hearing crashes as cars were struck from behind.
The car next to them "literally almost went under (a) semi truck," he said. "We saw that guy die after talking to him before we could even react."
He said the car he was riding in was then struck twice, effectively wedging it between two semis. He was not hurt badly, but his friend could "barely even move," he said. Camps helped pull him from the car onto the median.
"As it was happening on the northbound side, it was happening on the southbound side as well," he said. "There was nowhere to go. It was just cars hitting cars and cars."
He called the scene "horrendous."
"Everybody was crying," he said. "You still can't see anything." Some motorists were stuck in their vehicles, he said, calling it "mass chaos."
Camps said he received stitches in his leg and was released from a hospital. He said his friend was still hospitalized but may be released soon. He said he was "blessed" -- "If you saw the car, you'd be like, 'How did you live?' "
The crashes occurred between 11:30 p.m. Saturday and 4 a.m. Sunday in the same areas, Kelly said. A responding officer reported that visibility was virtually zero, he said.
Shands Hospital at the University of Florida received a total of 18 patients, said Dr. Timothy Flynn, chief medical officer. Of those, six were "trauma alert" patients who remained in the hospital's intensive care unit Sunday, he said.
Eight of the remaining 12 were treated and released, he said, while four others remained hospitalized for observation. The hospital, a Level 1 trauma center, activated its trauma alert system about 5:30 a.m., calling in additional staff, Flynn said.
The Florida Highway Patrol said Monday that a total of 21 people were taken to hospitals.
A dozen or more vehicles were involved in the crashes, Kelly said, describing the scene as "pure chaos" and the worst he has seen in his 14 years of service.
The smoke is from a brush fire at the nearby Paynes Prairie Preserve State Park, he said. Darkness was also thought to be a "contributing factor" in the crashes, Kelly said.
Both I-75 and U.S. 441 had been closed because of low visibility -- and then reopened -- before the crashes occurred, Lt. Riordan said.
He added that he did not know exactly when the roads were closed, how long they were closed or when they were reopened.
CNN's Rich Porter, Jacqui Jeras and Darrell Calhoun contributed to this report.