At least four people were killed and eight others, including children, were injured Sunday after a gunman opened fire inside a Latter-day Saints church in Michigan and then set the building ablaze, authorities said.

Officials confirmed that two of the victims were fatally shot, while two others were discovered inside the burned structure. Investigators cautioned that the death toll is expected to rise, as several individuals remain unaccounted for and additional victims may be found in the rubble.

The fire reduced the church to its foundation, complicating recovery efforts. Emergency crews suspended the search late Sunday night and are expected to resume clearing debris early Monday morning.

Officials said they do not yet know how many parishioners remain unaccounted for. A source familiar with the investigation told CNN the number could be as high as seven, though that estimate may include survivors who have not yet been able to contact their families.

FBI Director Kash Patel noted he was monitoring the situation and had been briefed on the attack.

Hundreds of worshippers had gathered inside the Church of Jesus Christ of Latter-day Saints in Grand Blanc Township when gunfire erupted. Moments later, images captured the building engulfed in flames, its frame swallowed by thick smoke and fire.

“We do believe there were people up there that were near that fire, and they were unable to get out of the church. So we do believe that we will have additional victims once we’re able to search that,” Grand Blanc Township Police Chief William Renye told reporters.

Police said the gunman, identified as 40-year-old Tomas Jacob Sanford, drove his pickup truck through the church’s front doors around 10:25 a.m. before opening fire with an assault-style rifle. The vehicle had two large American flags in its bed and deer antlers mounted on the front bumper.

Sanford was killed in an exchange of gunfire with a Grand Blanc Township police officer and a Michigan Department of Natural Resources officer who arrived on the scene within seconds of the first 911 calls.

Officials said the suspect was neutralized roughly eight minutes after the attack began, the New York Post reported.

Authorities said eight gunshot victims remained hospitalized Sunday night, including one in critical condition, according to Grand Blanc Township Police Chief Ron Renye.

James Deir, special agent in charge with the Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators believe Sanford used gasoline to ignite the blaze. He added that “suspected explosive devices” were also recovered at the scene, The Post noted.

Witnesses described the chaos that followed the truck crashing into the building. Congregant Kristin Juarez, 54, told The New York Times she initially thought the chapel’s steeple had collapsed before gunfire erupted inside the church, located about 60 miles northwest of Detroit.

She said she became separated from her husband and hid in a bathroom until she heard him calling her name.

“I thought, ‘If I have to die, it’s OK,’” Juarez told reporters. “I feel good about where I am,” she added as she described her thought process upon hearing her husband’s voice.

John Juarez, 57, said he helped carry an injured congregant outside before returning to the sanctuary, where he saw another victim lying on the floor with a gunshot wound.

“I didn’t know what I could do for him,’’ Juarez said. “I couldn’t get him out on my own.”

Paul Kirby, 38, said he rushed outside thinking the crash was an accident, but from about 10 to 20 yards away he saw Sanford climb out of the truck and quickly realized what was unfolding.

“He started shooting at me,” Kirby said, adding that a bullet ripped through a nearby glass door, cutting his leg with a piece of it.