A year 7 student seriously injured after being trapped under a train at North Melbourne station on Monday fell onto the tracks after his school bag became snared on the carriage.

“The student was standing with friends close to the edge of the platform as a train arrived at the station,” St Aloysius College principal Mary Farah said in a note to parents on Tuesday.

Emergency services workers strive to free the boy from under a train in North Melbourne on Monday.© Nine News

“The student had their back to the track and their school bag became caught on the train, causing the student to fall onto the track.”

Farah said another student pressed the emergency button on the platform to alert station staff and called Triple Zero, while other students spoke with transport officials. The principal said she was in close communication with the family of the injured student, who remains in hospital with injuries to his lower body.

“Platform 6 was very crowded, with a large number of students from St Aloysius College, along with students from other nearby schools,” Farah said.

In a statement to the media, Farah said the school’s thoughts and prayers were with the student and his family.

“The wellbeing of students, staff and the wider community remains the college’s priority,” she said.

St Aloysius staff were briefed on Tuesday morning about the incident and stood at the school gate as students arrived.

Emergency services worked for up to an hour to free the teenager from underneath the train on Monday afternoon.

Ambulance Victoria paramedic Alex Hemsley said on Monday evening that eight paramedics, along with firefighters, safety extricated the boy from underneath the train.

“Although we are all trained to do this job, [it was a] very traumatic scene for all involved,” she said.

The boy was taken to the Royal Children’s Hospital in a critical condition. By Tuesday morning, he had improved to a serious but stable condition, a hospital spokesperson said.

Metro Trains said the incident was being investigated.

“This is a tragic accident involving a young student, and our thoughts are with his family, friends and school community,” a spokesperson said. “We thank emergency services and staff for their quick response.”

Rail, Tram and Bus Union Victoria branch secretary Vik Sharma said the incident was an important reminder for people to be careful and safe around trains.

“Rail workers are often among the first to respond in traumatic circumstances, and events like this weigh heavily on drivers, station staff, authorised officers, signallers and all those involved in the response and recovery effort,” Sharma said.

“The [union] has been on site supporting members and will continue providing assistance to affected workers and their families. Our thoughts are with the family and loved ones affected by this tragic event.”

The Office of the National Rail Safety Regulator said it sent rail safety officers to North Melbourne on Monday to inspect the scene, and was seeking information from Metro about the incident.

Last month, a 12-year-old student was dragged by a bus along a road in Wheelers Hill, in Melbourne’s south-east, when his bag became caught in the vehicle’s folding doors. The boy’s mother said her son was released only once the bus driver noticed and pulled over at the next stop.