In a freak accident Tuesday on a Milwaukee expressway, a minivan carrying a Chicago family burst into flames, killing five children and critically injuring the parents and another child.

The accident occurred when the minivan, driven by Duane "Scott" Willis, a minister at a South Side church, ran over a piece of steel that had apparently fallen off a truck.

The 18-inch steel bracket, which holds mudflaps on semitrailer trucks, punctured the van's gas tank and lodged in the tank. Sparks ignited leaking gas from the tank, and "within seconds" the 1994 Chrysler Voyager minivan burst into flames, according to Milwaukee County Sheriff's Sgt. David Iushewitz.

Trapped in the van and killed in the fire were Peter Willis, 6 weeks old; Elizabeth Willis, 3; Hank Willis, 7; Sam Willis, 9; and Joe Willis, 11.

Duane Willis, 47, the minister at Parkwood Baptist Church, at 10435 S. Spaulding Ave., his wife, Janet Willis, 47, and their 13-year-old son, Ben Willis, escaped the crash with burns.

Shocked congregation members described the tragedy as "worse than losing a family member."

"I'm still in shock," said Mona Scott, 78, a neighbor and congregation member. "I can't believe it; five lives wiped out like that. They were a wonderful family, and I feel blessed that I got to know them. I just can't fathom going home and not seeing them."

Ben Willis was in critical condition at Children's Hospital of Milwaukee in Wauwatosa, Wis., Tuesday night with varying degrees of burns over 90 percent of his body, a hospital spokeswoman said.

The parents were in satisfactory and stable condition at Froedtert Hospital, also in Wauwatosa. They suffered first- and second-degree burns on their faces, necks, arms and upper extremities, according to a hospital spokeswoman.

With the church being used as a polling place Tuesday, the family was on its way to visit Dan Willis, another of the couple's nine children, who is a high school wrestling coach at the Maranatha Baptist Academy in Watertown, Wis., about 40 miles west of Milwaukee. The couple have two other adult children, Toby and Amy, according to neighbors.

The Willises were northbound on Interstate Highway 94 about 10:30 a.m. when the minivan, which was registered to the church, struck the metal bracket. The accident occurred just south of the Layton Avenue exit on Milwaukee's south side.

"I think just about all of us have hit something in the road before, a piece of tire or an animal or stick," said Dennis Hughes, chief of highway safety strategy and analysis for the Wisconsin Department of Transportation. "But it usually has much less severe consequences than this. It is very rare to have something so seemingly benign result in such a tragic outcome."

Milwaukee County Sheriff's Lt. Esther Moore, who was called to the scene, said officers had driven through the area minutes before the accident and saw nothing hazardous on the road. She said investigators are trying to determine where the piece of metal came from.

Willis, who was generally called Scott, had been the minister at Parkwood, in the Mt. Greenwood neighborhood, for seven years, neighbors said. The family moved from the Brighton Park neighborhood and converted the second floor of the church into their living quarters, according to 24th Ward precinct captain Joe Coglianese.

Church members said Willis was also an elementary school teacher at Dawes School.

Jamie Susnis, who joined the church in January, stopped by late Tuesday afternoon hoping to hear news of what had happened to the pastor's family.

Susnis joined the church seeking solace over her 2-year-old daughter's heart condition.

"They prayed for my daughter," Susnis said of Scott and Janet Willis. "They're just wonderful people. They're just very family-oriented."

Janet Willis had become a role model for her "by showing me what a great mother she was of nine children."

Congregation member Gail Halleran described the minister's children as "wonderful, well-behaved Christian kids." She doesn't know if she will be able to set foot in the church again.

"That's all I have sat and thought about since I heard," she said. "The Willis kids did a lot of things, sang, put on programs and stuff. I can't see what it would be like without his children."

Halleran and other members credited the Willises with reviving the once-dormant Baptist church in a heavily Catholic neighborhood after arriving seven years ago.

Gerilynn Lathrope, who has belonged to Parkwood all her life, said the Willises recently officiated at the funeral of a newborn girl, the granddaughter of a church member.

"Janet had told me how devastating it was and that she picked up Peter, her newborn, and held him and was just so thankful that he was healthy and OK," Lathrope said, choking back tears. "She didn't want to put him down."

Janet Willis educated her children at home, church members said, because she didn't want them to learn about evolution and other theories that conflicted with the family's religious beliefs.

Congregation members recalled that the children loved to play sports, especially baseball, football and wrestling, to put on skits in church, and to sing religious songs around a piano at home.

David Arenz, 10, who lives at 10538 S. Spalding Ave., said he used to play football and baseball with Ben and Joe Willis.

"I feel bad," he said.