More than 30 people were injured when a New Jersey Transit bus rear-ended a private bus carrying Canadian schoolchildren inside the Lincoln Tunnel on Wednesday.

The accident, which occurred at around 9:30 a.m., also caused a traffic jam on one of the busiest routes in New York City, the Associated Press reported.

Joe Pentangelo, spokesman for the Port Authority of New York and New Jersey police, said that the crash occurred in the center part of the tunnel.

Anna Caputo, spokeswoman for the Toronto District School Board, said no injuries were reported for the 26 students and two adults from the Toronto District School who were going for a graduation trip, according to NBC New York. 

Meanwhile, around 35 to 40 out of 60 passengers of the NJ Transit bus heading from Cresskill, N.J., to the Port Authority Bus Terminal were hurt, while four are severely injured. 

The New York Fire Department said that around 31 people were brought to the hospital with injuries that are not life threatening.

A 32-year-old woman was also brought to the hospital after having labor while stuck in the tunnel. Other passengers and commuters who were stuck in the tunnel were informed about what was happening by a police officer that was walking from bus to bus to give updates, Newsweek reported.

Passengers were stuck on the bus for 10 to 20 minutes because the door was bent, said one passenger, Jaehoon Chung, a carpenter from New York.

The tunnel consists of three tubes built beneath the Hudson River that over 42 million vehicles travel through each year.