A nine-year-old boy has been "significantly injured" after an inflatable zorb ball he was in was 'raised into the air' before landing on the ground.
The incident happened at Southport Food and Drink Festival at around 2pm on Sunday 4 June.
Merseyside Police say the boy was in the inflatable ball on a lake when he was "unexpectedly raised into the air before it landed on the grass".
The schoolboy was taken to hospital by air ambulance where he remains, the force added.
A second ball containing another child was also raised into the air at the same time, but the child was unharmed.
Police are investigating the cause of the incident, amid reports that the zorb was blown by a gust of wind and are urging anyone with video or images of the incident to come forward.
In a statement police said: "We are appealing for information after a child was seriously injured today in Southport.
"At around 2pm on Sunday 4 June, it was reported that a nine-year-old boy had sustained significant injuries at an outdoor festival in Victoria Park, on Rotten Row.
"The boy was inside an inflatable zorb ball on a lake, which was unexpectedly raised into the air before it landed on the grass.
"A second zorb ball containing another child was also raised at the same time, but thankfully this child was unharmed."
Sefton Council confirmed the incident had happened, adding following "a full health and safety inspection" the event remained open.
It added: “Our thoughts are with those involved in the accident and we wish them a full recovery.”
A North West Ambulance Service spokesperson said: "We were called at 1.56pm today. We did attend with an ambulance, a senior clinician and an air ambulance.
"A patient has been air-lifted to hospital with multiple serious injuries. They arrived at the hospital around 3pm."
Anyone with images of videos can upload them here.
Those with information are asked to DM @MerPolCC or @CrimestoppersUK on 0800 555 111 quoting reference 596.