NORTHFIELD TOWNSHIP, Mich. -- A tractor-trailer crashed into an overloaded bus carrying members of an Amish church, sending at least 14 people, including a number of children, to a hospital in nearby Ann Arbor.

Michigan State Police Trooper Randy Phare said none of the injuries are believed to be life-threatening and most are cuts and bruises.

Four adults and two children were in serious condition at the University of Michigan Hospital in Ann Arbor, spokeswoman Kara Gavin said.

Phare said 21 people, ranging from infants to elderly, were in the 13-seat bus when the bus driver was trying to avoid a slower vehicle entering southbound U.S. 23 in Washtenaw County's Northfield Township before 1 p.m. Thursday when the bus swerved left in front of the truck.

The truck hit the back of the bus, which rolled on its side and skidded along the highway 40 miles west of Detroit. Another vehicle then ran into the back of the stopped truck.

The 24-foot bus, that was turned into a motor home, tipped on its side and came to a rest in the right lane.

Phare said he was not sure if the seat belts were being worn.

"Obviously rolling over inside the vehicle, with everything being loose in there, the smaller children not being restrained in seats, and things like that, that's where most of the injuries came from," said Phare.

Dianna Clinansmith said she saw the church members helping each other out of the back of the bus after the accident. Clinansmith said she and a neighbor tried offering them assistance, but they did not respond.

The freeway was closed for a portion of the afternoon while police conducted an investigation, but re-opened at about 2:45 p.m.

The Mount Pleasant-area church members were headed to a funeral in Ohio, Phare said.

"It could have been a lot worse," he said, pointing to the truck's size and speed. He estimated the truck was traveling between 60 mph and 70 mph.

The driver of the bus was not Amish. Police are trying to determine if the driver was hired or was a friend.

Motor vehicle laws will be researched to determine if charges will be filed against the bus driver, Phare said.