The crash happened about 10.20am on Thursday (local time) in Mount Olive Township in northern New Jersey’s Morris County, Governor Phil Murphy told media.
The bus was carrying 38 pupils from the 5th grade (aged 10 and 11) and seven adults, including the driver.
“Some patients are in critical condition and currently undergoing surgery, so please keep everybody in your prayers,” Murphy said.
“There is an awful lot we just don’t know,” the governor said, adding details of the crash are not being released pending an investigation.
The front end of the bus was ripped from the vehicle and the body of the bus separated from its chassis, which remained on the road. The rubbish truck seemed to be mostly intact.
The bus was carrying students from East Brook Middle School in Paramus to Waterloo Village, a restored 19th century canal town, officials said.
“The bus flew off of the wheels, but it hit the metal thing on the side of the highway,” pupil Theo Ancevski said.
He told reporters he escaped through an emergency door on the bus.
“A lot of people (inside the bus) were screaming and they were like, hanging from their seat belts."
The crash temporarily shut all westbound lanes of I-80, State Police said.
“The children were all over, outside,” said Morris County Office Of Emergency Management Director, Jeff Paul.
“We had every injury type that you can imagine for a scenario like this. It’s tragic."
Two other buses in the field trip convoy also carrying fifth-graders on the same trip returned to Paramus, officials said.
The National Transportation Safety Board, which investigates accidents involving buses, was gathering information on the crash but was not investigating the collision, the agency said on Twitter.
Paramus is about 15km west of upper Manhattan. Mount Olive is about 40 miles west of Paramus.
