Firefighters were called to Hornchurch Country Park shortly after 2pm yesterday (January 7) after reports of a child stuck on a riverbank.
Three fire engines and two fire rescue units attended the scene and were able to rescue the child.
They were then treated by London Ambulance Service before being taken to hospital.
It is not clear whether the water was frozen when the rescue took place.
A spokesperson for the London Fire Brigade (LFB) said: “We were called at 14.06pm yesterday (7 January) to a report of a person stuck on a river bank at Hornchurch Country Park.
“Firefighters attended and rescued a child before leaving him in the care of London Ambulance Service.
“Three fire engines and two fire rescue units attended the scene.”
A London Ambulance Service spokesperson added: “We were called at 2.10pm on Wednesday 7 January to reports of an incident at Hornchurch Country Park, Hornchurch.
“We sent resources including an ambulance crew, an incident response officer and paramedics from our hazardous area response team (HART).
“We treated a child at the scene and took them to hospital.”
