The Front Street Baptist church van crashed head-on into a tractor trailer and SUV on Wednesday, causing a shutdown on a major Tennessee interstate. At least eight people were killed in the crash, and 14 others were critically injured. NBC's Janet Shamlian reports.

The National Transportation Safety Board is not sending anyone to investigate a horrific Tennessee bus crash that left eight people dead and 14 more injured because the government shutdown furloughed all its highway investigators, an NTSB official said.

“In this particular case I think it’s highly likely that we would have responded to it, but again, with our investigators furloughed, it’s impossible to do that,” Sharon Bryson, deputy director of communications for the NTSB, told NBC News.

“All of our highway investigators are furloughed,” Bryson said.

Eight people were killed after a bus carrying members of a church in North Carolina overturned around 2 p.m. ET Wednesday, officials said. The bus was carrying members of the Young at Heart program at Front Baptist Church in Statesville, N.C., who were headed back from an annual preaching and gospel music conference in Tennessee, the church said.

The 14 people injured in the accident were described as senior citizens.

The crash appears to have been caused by an issue with the bus’ front tire as the vehicle traveled along Interstate 40 east of Knoxville, said Sgt. Bill Miller, a spokesman for the Tennessee Highway Patrol, in a news conference Thursday morning.

The bus crossed the median and rammed into a tractor-trailer vehicle and an SUV carrying three people before turning over on its side and setting the tractor-trailer ablaze, according to Miller. Six people on the bus were killed and one person died in each of the two other vehicles.

The University of Tennessee Medical Center in Knoxville treated 14 elderly patients, two of whom were still listed as being in critical condition late on Wednesday. Seven more were in serious condition, and the rest were considered stable.

Paul Efird / Knoxville News Sentinel via AP Emergency workers respond to a crash involving a passenger bus, a tractor-trailer and an SUV near Dandridge, Tenn., on Wednesday.

“We saw bodies all over the ground and some people walking around," said Fred Lucas, who stopped to lend assistance on Wednesday.

Lucas and his wife, who are doctors at the University of Cincinnati Medical Center in Ohio, were driving to Asheville, Tenn., when they spotted the smoke from the crash, The Knoxville News reported.

Their doctors' instincts kicked in, and both Lucases began helping with a makeshift triage effort.

"Just get them away from the fire — figure out who was alive and who was dead and get the live ones first," Lucas told the newspaper. "I didn't even stop to figure out who was who. There wasn't any time for that."

NTSB Chairman Debbie Hersman had confirmed to NBC News on Wednesday night that the board -- which is tasked with investigating significant accidents in the air, on highways, and on the water – would not deploy anyone to the site of the Tennessee crash. A spokesman for the Tennessee Emergency Management Agency said that officials in the state requested NTSB assistance overnight.

Miller described the damage to the bus as “tremendous” on Thursday.

“Some of the identifications of the individuals involved in this incident, involved in this crash, it’s not very easy to discern who they are, the crash is so horrific,” Miller said, adding that some of the individuals may need to be identified by their dental records.

“It’s probably the worst that I’ve seen in my career,” said Miller, a 17-year veteran.

The Tennessee Highway Patrol is leading the investigation into the crash, and will look at factors including the speed the bus was traveling, service records for the bus, and the driver’s history, Miller said on Thursday.

“We’re in the very first stages of this investigation,” Miller said.

NTSB investigators responding to an incident like Wednesday’s bus crash would usually spend a week or two on the scene, Bryson said. Compiling a final report would take about 12 months on average, she said. As for what they would have found if the NTSB had made an investigation of the Tennessee crash, Bryson said that will likely remain unclear.

“I think it’s hard to say,” Bryson said. “Without being able to take a look at it, it’s really hard for us to know.”

NBC News’ Tom Costello, Niven McCall-Mazza and Edgar Zuniga Jr. contributed to this report.