(CNN) -- Three people were killed and 19 injured when a bus carrying about 40 passengers to an Indianapolis church overturned Saturday afternoon.
"I saw bodies everywhere, kids in shock and disbelief," said John Murphy, who had stopped along the northern Indianapolis road. "There was an awful lot of blood."
The bus was returning from a camp in Michigan, said Indianapolis Mayor Greg Ballard.
Among those killed were the youth pastor for Colonial Hills Baptist Church, Chad Phelps, and his wife, Courtney, said Jeff Leffew, a church deacon, at a press conference Sunday. Courtney Phelps was pregnant, and the couple were expecting their second child next month, Leffew said.
Tonya Weindorf, a mother of five who was a chaperone on the trip, also died, he said.
"They are with God in heaven right now. We know that without a doubt," Leffew said, "but we grieve for the fact that they are not here with us."
The deacon asked for prayers and support as the church and victims recover.
"We're going to have a long road," he said.
Most of those on board were teenagers, according to Indianapolis Fire Department spokeswoman Rita Burris.
The driver told witnesses that the vehicle's brakes failed as he was trying to make a left turn, she said.
The bus ended up on its side on a concrete road barrier with luggage and other debris strewn on the roadway.
Indianapolis police spokesman Michael Hewitt said two passengers were airlifted from the crash, nine were treated and released at the scene of the accident and others were taken to local hospitals.
Seven teenagers are being treated at the main hospital and children's hospital at Indiana University Health, according to Sally Winter, public relations coordinator for IU Health. One is in critical condition, and the six others are in good condition, Winter said.
The bus is believed to be the only vehicle involved in the crash, according to Hewitt.
"Please pray for all involved," the Indianapolis Fire Department tweeted.
Rose Vorenkamp was driving when she saw the overturned bus and saw "people running" to help. Having been trained through her job in first aid and CPR, she moved closer and saw what she described as a girl trapped under the bus, bloodied passengers with head injuries and at least one person with a dislocated shoulder.
The fire department noted that four passers-by arrived first to help, including one who helped pull the driver from the bus.
Those helping were met soon by firefighters and crews from 12 ambulances and four helicopters.
By then, traffic in the area had been shut down, and all the casualties had been sent to local hospitals. Family members subsequently gathered at the church, Colonial Hills Baptist, where the bus had been heading.
The scene there was "remarkably positive, very sad, but at the same time very together," Ballard said.
"Some of the teenagers are hurting very badly; you can see it in their faces," the mayor said.
Some people at the church thanked him for visiting and generally appeared strong, Ballard added, surmising that "it's very clear that they are being guided by their faith right now."
Still, the mayor added, they might have some tough days ahead of them.
"The next few days are always very, very painful as they come out of the shock of it," he said.