Multiple accidents in a one-mile section on the Tri-State Tollway kept firefighters and state police officers scrambling early Tuesday morning, authorities said.

The worst of the crashes took place in the southbound lanes when four semitrailer collided at the Route 21 overpass near mile marker 10, Gurnee Fire Department Lt. Heath Graham said.

The semis rear-ended each other for an unknown reason at 9:59 a.m., he said. One truck driver was injured and transported to a hospital with a head injury, Graham said.

The accident resulted in a complete shutdown of southbound I-94 for approximately two hours. The roadway was reopened to one lane of traffic at 12:04 p.m., and a second lane of traffic about 12:30 p.m.

Two right lanes of the roadway remain blocked for investigators to work but all lanes had been reopened by 6 p.m., officials said.

Graham said the cab of one of the trucks caught fire and flames spread to its trailer. The trailer was hauling coupon mailers, and each pallet of paper had to be removed and individually doused by firefighters, Graham said. The cause of the fire remains unknown and is under investigation, he said.

In addition, a second truck had a diesel leak that was contained and cleaned, Graham said.

The truck crash came on the heels of two separate vehicle accidents Tuesday at mile marker 10, Graham said.

The first took place at 9:36 a.m., and was followed by another at 9:50 a.m. Each involved a passenger car, but there were no injuries, Graham said. It's unclear if either of the first two accidents caused the later semitrailer crash, he said.

Officials from the state police said one semi crashed into a median wall before the fire started in the area. However, officials from the state police have been unavailable throughout the day to provide details.