A Trinity College student has been hit by a train at the Tambelin Railway Station, in Adelaide's north.
Police said the 11-year-old boy was conscious and breathing after being struck at Evanston Gardens at about 8:15am.
The boy was taken to the Women's and Children's Hospital in a critical condition.
The line between Elizabeth and Gawler has since reopened.
In a message sent to the school community, Head of Trinity College Nick Hately said a number of Trinity students and staff witnessed the year seven student being struck by the train.
"This is a very distressing time for our community and of course the family of this student," he said.
"The safety and wellbeing of our students is always our top priority, and we are deeply saddened by this event.
"We ask you all to keep this student in your thoughts and prayers as they receive medical treatment."
Mr Hately said "appropriate briefings" were taking place for students and staff and that pastoral and counselling teams were available and offering support as required.
University students Sophie Shepley and Morgan Taylor were on the train when it hit the boy.
They said passengers on the train did not know what had happened until people on the platform started banging on the windows and then they could see a person had been hit.
"It was really confusing. We just didn't know what to do," Ms Shepley said.
Ms Taylor felt for the train driver.
"These things are difficult and hopefully he's OK," she said.
The train line had earlier been closed between the Elizabeth and Gawler stations.
Clark Road, which crosses the railway line at the Tambelin station, was earlier closed to traffic but has since reopened.
Three pedestrians died after being hit by trains in Adelaide last year, including one on the Gawler line, which reopened in June after being closed for 18 months for electrification work.
Education Minister Blair Boyer said CCTV at the station would be reviewed to see if safety could be improved.
"If there's anything, I guess, mechanically, at the site that needs to be changed to improve safety, we can do that," he said.
"My thoughts are with the young person in this case and with their family as well, there's no doubt this is an incredibly tough time for them."
Improvements to the car park at the station worth $530,000 were included in the 2022–23 state budget.
Mayor calls for more automatic gates
There are no automated pedestrian gates at the station — a situation that Gawler Mayor Karen Redman would like to see changed.
Ms Redman, who said the "entire community of Gawler is thinking of" the young child involved, said she intends to write to Transport Minister Tom Koutsantonis suggesting automatic pedestrian gates be installed at "all of our train stations".
"It is now really quite critical that the state government install automatic gates because I think that might have prevented this type of incident, and I will be writing to the minister lobbying to get these types of gates," she said.
"Tambelin is a really popular train station, it's got a bigger-than-average car park … it's well-known in Gawler that many students use that train station.
"We need to protect our children and we need to put in all safety measures, and this may be a way of preventing similar types of incidents in the future."
In response, Mr Koutsantonis — who said his thoughts were "with the student, his family and friends" — said the rail line's operator will conduct "its own thorough review of all circumstances in today's events" and provide a report to the Department for Infrastructure and Transport.
"It's extremely disappointing to see the Gawler mayor passing comment on the circumstances of this incident at this time, and while a police investigation is ongoing," the minister said.
Mr Koutsantonis said the number of "passive crossings" — which do not have automated pedestrian gates — across metropolitan rail networks is more than 240, "and all of these meet Australian railway safety standards".
"The average cost of activating a passive crossing is around $4 million, so there is a significant cost attached to what the mayor is proposing today for the entire line," he said.
