Updated

Two adults and two children, believed by police to be a family, were found shot to death Friday morning along an isolated stretch of Florida's Turnpike in St. Lucie County, with the woman clutching the two children in an apparent attempt to protect them, authorities said.

A witness alerted Florida Highway Patrol troopers to the bodies of a man, woman, boy and girl on the southbound shoulder south of the Route Midway Road in Port St. Lucie around 7:45 a.m., according to the St. Lucie County Sheriff's Office.

Investigators believe the victims' vehicle had pulled to the side of Florida's Turnpike before someone else in the vehicle shot them and drove away sometime between 1:30 and 3 a.m., Sheriff Ken Mascara said.

"They were killed by multiple gunshot wounds," Mascara told reporters Friday afternoon.

The sheriff would not say whether investigators knew of a motive or had any suspects. The vehicle left tire tracks as it pulled away, Mascara said.

The names of the 29-year-old man and 25-year-old woman were withheld until relatives could be notified. The children were between 4 and 6, he said.

"It appears to be a Hispanic family," Mascara said, even though the last names of the adults don't match. "The female had both the children clutched in a defensive mode, in an attempt to protect them. It gives the appearance that they were a family traveling."

Mascara told reporters the suspect — or suspects — likely continued driving south after the shootings.

"There's no risk for anybody in the immediate area," he said, adding that the crime appears to be "very transient in nature."

No vehicle was found near the bodies, but there were tire tracks from a vehicle that apparently pulled back from the scene and sped back onto the turnpike, Mascara said.

"You can stand back and see someone has driven off the road," Mascara told The Palm Beach Post.

The bodies were spotted in a grassy area near the St. James Golf Club, several miles away from the nearest rest stop, the sheriff's office said. There was a surveillance camera around the corner, but it wasn't turned on, Mascara said.

Tracy Maynor, staff clerk at the golf club, said a resident of the homes along the golf course reported hearing "some shots or fireworks at about three in the morning. That's about all we heard."

Cameras posted along the turnpike were not recording at the time, Mascara said.

A blue tent was set up over the bodies and white material covered them until they were released to the medical examiner.

An autopsy was scheduled Friday afternoon. A message left at the medical examiner's office was not immediately returned.

Janis Rich, a 67-year-old retired bookkeeper, said she her husband were asleep in their golf club home, a quarter-mile from the scene, when they awoke to a loud "pop-pop-pop-pop" sound from the direction of the turnpike just before 2:30 a.m.

Rich said the couple saw no traffic or anything else in the darkness. "We were trying to hear anyone speaking, anyone crying, but it was total quiet," she said.

An FHP spokesman referred calls to the sheriff's office.

"Florida's Turnpike is the main toll road connecting the Miami area with cities along the Atlantic Coast to Fort Pierce and then inland to Orlando and Interstate 75.

The Associated Press contributed to this report.