'I saw a big mushroom cloud': Clues sought in Virginia shopping center explosion that rattled residents for miles.

Investigators on Sunday hunted for clues behind a thunderous explosion that leveled a strip mall, injured five people and rattled residents for miles on a peaceful morning in Virginia's Shenandoah Valley.

The blast Saturday ripped through a shopping center in downtown Harrisonburg where businesses included a family owned halal market, a musical instrument store and recording studio and a nail salon and barber shop.

Nearby James Madison University said in a Facebook post that three students from the school’s Army ROTC program who had been participating in a 10-mile race were among the injured. The explosion occurred about 30 yards from the start and finish line for the race, the school said.

Damon Boyd, who was working construction nearby when the blast erupted, told the Daily-News Record he and his crew rushed to the scene. An injured man on the ground “started hollering that he's dying," Boyd said. "It looked like something hit him in the face."

Although Gov. Ralph Northam tweeted that state emergency personnel had been deployed to the area after what he called a gas explosion, Harrisonburg Fire Chief Matt Tobia said the cause was under investigation.

City spokesman Michael Parks, who said the probe will likely take several days, said there’s no indication of foul play.

Investigation underway: Investigation underway after explosion injures several people at a Virginia shopping center

One of the injured JMU students was hospitalized but was expected to be quickly released, the university said. Two other students were treated at the scene and released, the school said.

The university said the other two injured people were not affiliated with JMU. City officials said the two others had been flown to the University of Virginia’s medical center in serious condition and were “now stable.”