Minutes before two pileups killed 10 people on a highway shrouded in fog and thick smoke from a brush fire, the Florida Highway Patrol had reopened the always busy six-lane interstate after an earlier serious accident.

A sergeant and lieutenant determined after about three hours that conditions had cleared enough for drivers, but visibility quickly became murky again, officials said Monday.

"We went through the area. We made an assessment. We came to the conclusion that the road was safe to travel and that is when we opened the road up," Highway patrol spokesman Lt. Patrick Riordan said in a news conference. "Drivers have to recognize that the environment changes. They have to be prepared to make good judgments."

At least a dozen cars, six tractor-trailers and a motorhome collided at about 3:45 a.m. Sunday. Some cars were crushed under the bellies of big rigs. Others burst into flames and sent metal shrapnel flying through the air, horrifying witnesses watching the violence along Interstate 75 in calls to 911.

Eighteen survivors were hospitalized.

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In a 911 recording released Monday, a driver and her passengers told a dispatcher that the fog and smoke from the 62-acre brush fire was so thick they couldn't see.

"I think there was another accident behind us because I heard it," a woman said. "Oh my gosh, it's so dark here."

Late Monday, the highway patrol said seven people died and at least 16 people were injured after 10 vehicles crashed in the northbound lanes of the highway, the first of two multiple-vehicle pileups along I-75.

The vehicles crashed about 4 a.m. after driving in heavy smoke that made it hard to see. Jason Lee Raikes, 26, of Richmond, Va., died in the crash, authorities said.

They also said five out of six people riding in a 2012 Dodge Caravan died in the crash: Driver Edson Carmo, 38; Roselia DeSilva, 41; Jose Carmo Jr., 43; Adrianna Carmo, 39; and Leticia Carmo, 17; all of Kennesaw, Ga. The highway patrol did not immediately provide the identity of the seventh crash fatality.

Jose and Adriana Carmo were married and Leticia was their daughter, said Arao Amazonas, senior pastor at their church, the Igreja Internacional de Restauracao, or International Church of the Restoration.

The van's sixth occupant, the couple's younger daughter, Lidiane, 15, survived the crash, Amazonas said. A hospital spokeswoman said Monday afternoon that she was listed in critical condition.

Amazonas had been at a religious conference in Florida with the family and many others since Thursday. He said he spoke with the pastor before the family left Florida on Saturday night and urged him to wait until morning, he said. But Carmo told him he wanted to be back in time for the Sunday morning service.

The Carmos were in one van and other church members were in a second van. The passengers of that van called Amazonas after the accident to tell him what happened, he said.

About 100 people gathered Monday evening at the suburban Atlanta church, which caters to the local Brazilian community, to mourn the deaths of their fellow church members. People at the gathering wailed and wept as Amazonas addressed them in Portuguese.

"We couldn't have imagined such tragedy would come to us," Amazonas said.

Riordan declined to release the names of the two troopers who made the decision or provide details on how long they had been with the patrol. He said no troopers have been disciplined but the investigation into the crash continues. National Transportation Safety Board officials said Monday they are sending investigators to the scene. Gov. Rick Scott also called for an investigation.

In the same 911 call, another woman took the phone and screamed an expletive as she hears another crash.

"That was a truck. We cannot see. It's like impossible to see," the caller said. "The smoke is very thick you can see obviously only your hand in front. I do hear an ambulance or police officer coming down the road."