Fire crews were dispatched around 2:50 Wednesday afternoon to Yorklyn and Old Wilmington roads in Hockessin.
Initial reports indicate that there were about 35 students onboard the bus from the Red Clay School District.
A district spokesperson said the bus driver noticed smoke or steam coming onto the bus and pulled over. The students were then taken off the bus while another one was called.
No injuries have been reported. Authorities are not sure what caused the smoke.
Officials say the original bus is being checked out to determine what happened.