"We thought it was just a drill and people were joking around", said student Alejandro Garcia.
Faltings said first responders pulled children from the mangled bus.
K-9 units were seen searching wooded areas near the crash scene, NBC 4 NY reported. Morristown Medical Center spokeswoman Elaine Andrecovich told the AP the hospital has received some people from the accident, but she did not have a number available and could not say how many were children. It is unclear how many people died.
She said students did not find out about the accident until they arrived back at school. He says he thinks something hit a vehicle behind the bus.
"I heard a scraping sound and we toppled over the highway", said student Theo Ancevski, who was sitting in the fourth row of the bus and was treated at a hospital for cuts and scrapes. Some of the victims crawled out of the emergency exit in the back of the bus and an escape hatch on the roof.
Injured passengers were taken to Morristown Medical Center, St. Joseph's Hospital and Hackettstown Medical Center, according to the school district. The bus was headed to Waterloo Village as part of a field trip.
This image taken from WABC-TV video shows an overturned school bus after it collided with a dump truck, injuring multiple people, on Interstate 80 in Mount Olive, N.J., Thursday, May 17, 2018.
The National Transportation Safety Board said via Twitter that it was "gathering information" on the crash.
"It's a horrific scene", he said.
Gov. Phil Murphy said at least one student and one teacher were killed in the crash.
Students at East Brook Middle School, a public school serving roughly 650 students in grades 5 through 8, were picked up early from school - they found out about the accident when other students were crying in the halls. He calls the crash a "tragedy".
A state prosecutor confirmed "fatalities", after the crash, in which 43 others were injured. She said she rushed to the school after hearing the news.
The bus was apparently filled with children, and multiple injuries are reported.
The body of the bus came completely off its chassis and was resting on its side in the highway median.
The extent of the injuries was not immediately known.
The students were on the way to Waterloo Village from the middle school when the collision happened.
A school bus that collided with a dump truck in New Jersey had markings for a school district that had a scheduled class trip to a nearby historic site.