A woman in her 40s is in hospital with life-threatening injuries after a funfair ride malfunctioned at a country show in south London, the Met Police has said.
The incident happened during Lambeth Country Show in Brockwell Park at about 18:20 BST on Saturday.
A man in his 40s is also being treated for "potentially life-threatening injuries", the force said.
Lambeth Council said the investigation would "determine the cause of the malfunction".
Two other people, a man in his 50s and an 11-year-old girl, were injured in the incident and have since been discharged from hospital, the Met said.
The problem occurred during the first day of the free event.
Funfair rides at the show were closed on Sunday, the council added.