A group of school children have fallen from a five-metre-high structure during a field trip in the western Canadian city of Winnipeg but avoided serious injuries in an incident that officials say could have been much worse.

Children from Winnipeg’s St John’s-Ravenscourt School were visiting the historical Fort Gibraltar when the fall happened, sending 16 children and an adult to hospital.

The children were between 10 and 11 years old and suffered non-life-threatening injuries, Dr Karen Gripp of the Winnipeg Children’s Hospital said in a televised briefing.

One patient was being kept in hospital for observation while the rest either had been or will be discharged during the day, Dr Gripp said.

“It could have been so, so much worse,” she said.

“Fortunately, or serendipitously, it was not very busy and we were all caught up at the time so we had empty rooms, we had nursing staff available.”

Winnipeg Fire Paramedic Service official Michelle Bessas said the children fell from a structure at Whittier Park, where the fort is located. The reason for the fall is not yet clear.

The structure was approximately five metres high, she said, adding that paramedics assessed 28 patients, 17 of whom were transported to hospital.

“Our thoughts go out to all the students, teachers and families of St John’s Ravenscourt affected by today’s terrible accident at Fort Gibraltar,” Manitoba Premier Heather Stefanson said on Twitter.

Fort Gibraltar, in the province of Manitoba, is one of more than 1000 protected national historical sites in Canada.