State police Capt. Eric Janis said Thursday that 19 people were treated at three Binghamton-area hospitals after the Wednesday night accident.
The tour company said all the passengers were brought back to New Jersey, and Janies said police were trying to confirm that all the injured had been released.
The injured included a woman who was trapped beneath the bus and was dug out by emergency crews.
"They had to actually dig the dirt underneath the bus to free the lady," state police Sgt. Todd Burdick told WBNG-TV in Binghamton.
He told the Press and Sun-Bulletin of Binghamton (http://bit.ly/o8zxpG) that heavy rain and speed too fast for conditions caused the accident, which occurred around 7:10 p.m. Wednesday on a rural stretch of Interstate 81 near Whitney Point, about 15 miles north of Binghamton.
The bus was traveling from Niagara Falls to Trenton, N.J., when it left the highway's southbound lanes and went down an 80-foot grass embankment before overturning and landing on its roof in a gully, Burdick said.
Janis said it was raining heavily at the time, while other troopers said there was a half-inch of standing water on the road. The speed limit along that stretch is 65 mph, although investigators don't know yet how fast the bus was going before it crashed, Janis said.
He said the bus was removed from the crash scene and taken to an undisclosed location where the state police Commercial Vehicle Enforcement unit was conducting its investigation.
In addition to the driver and a tour guide, the bus was carrying 28 passengers, all of them tourists from Poland, Janis said.
Police identified the driver as Albert B. Moore Jr., 30, of Bensalem, Pa. The tour guide's name wasn't available, Janis said. Police said the bus was licensed to Princeton Holdings Inc. of Morrisville, Pa., which also owns the company that operated the tour, Trenton-based Amerpol Tours.
M.J. Stawowezyk, the tour company's general manager, said the group arrived in Niagara Falls on Tuesday afternoon and spent the night in a hotel on the American side of the falls.
Stawowezyk told The Associated Press on Thursday morning that the group spent Wednesday visiting tourist attractions on both sides of the falls before boarding the bus for the return trip to Trenton.
Stawowezyk said his company specializes in U.S. sightseeing trips for Polish tourists. He said he believed most of those on the bus were Polish nationals.
Both southbound lanes of I-81 were closed after the crash. The left lane reopened around 11:15 p.m., while the right was open again by 1:30 a.m. Thursday.
