ST. JOHNS COUNTY, Fla. -- The search is on for a shooter who has been taking aim at trucks traveling on Interstate 95 in St. Johns County.

Channel 4 learned Friday evening that the number of tractor-trailer rigs shot at on I-95 is more than twice what police said they originally believed, putting the total of big rig shootings at six.

The Florida Highway Patrol first reported it was investigating after three tractor-trailer rigs -- one a gasoline tanker truck -- were hit by gunfire overnight Thursday.

According to the Florida Highway Patrol, at least one bullet hit a gasoline tanker truck. About 50 gallons of gas were spilled before firefighters could plug the leak.

The tanker truck was driven to a gas station at the state Road 207 exit to wait while its 3,000-gallon load could be transferred to another tanker.

The driver of the tanker told investigators he was southbound near the county Road 214 overpass when saw the gas spraying out of the side of the tanker in his rear-view mirror. He said he saw headlights in the woods shortly before he noticed the leak happened.

Another trucker said he heard a loud bang and pulled over at a rest stop and saw a bullet hole in his door.

Troopers said when the driver pulled over he saw that a bullet had hit his passenger-side door.

Investigators said if the shot had hit the glass, it could have been much worse.

"Higher up, it could've went through the window and struck him. So, it's very dangerous," said FHP Lt. Bill Leeper.

The third trucker, who was driving a UPS truck, pulled over with engine trouble and found an oil pan had a bullet hole in it.

"It's very strange to have three vehicles struck like that accidentally, so more than likely it was intentional," said Leeper.

The big rigs were going southbound just past the state Road 16 exit when they were hit. FHP investigators have recovered some bullet fragments and believe a high-powered rifle was used in all three incidents.

Since the original reports, more truck drivers have come forward, and authorities said at least six trucks have been fired upon.

"I would simply tell you at this point that it's somewhere in between the state Road 16 and I-95 area south to the next ramp. We don’t want to be absolutely specific in that as again, our investigation is still ongoing as we attempt to recover evidence in that area," said St. Johns County Sheriff's Office Sgt. Chuck Mulligan.

Investigators are expected to send recovered bullet fragments to a lab to find out the caliber of bullets and from what kind of weapon they may have been fired.

A St. Johns County Sheriff's Office helicopter searched the area looking for whomever was firing the shots, but they did not locate anyone.

Without knowing the intentions of the shooter, investigators urge all drivers to be on the lookout.

"Be aware of your surroundings and if you see anything suspicious, note that in case something does happen," Leeper said.

Law enforcement officers have increased their patrol of the highway.

Anyone with information that could help police solve the case is asked to call the St. Johns County Sheriff's Office at 904-824-8304.