Twelve children and five adults were taken to hospital after a miniature train carriage overturned in a caravan park.
The incident at Drumhoney Holiday Park in Irvinestown, Co Fermanagh, happened around 11.30 am.
There were no serious injuries and all those taken to the South West Acute Hospital in nearby Enniskillen have now been released.
The train was on one of its regular trips around the park when the central carriage turned over.
Park owner Ivan Bradshaw said it was not clear what had caused the accident.
He said the train trips round the site were organised to raise money for charity.
"We just don't know what happened at this stage, it's under investigation," he said.
The Health and Safety Executive NI said it was liaising with the police and Fermanagh District Council over the incident.
A hospital spokeswoman said: "Five adults and 12 children were treated for minor injuries. All of them have been treated and discharged."