Police are investigating a collision involving two all-terrain quad bikes on Barmouth beach.
One man was seriously injured following the incident involving red and green coloured quad bikes at just before 7.10pm on Saturday morning.
He was airlifted to a specialist trauma unit at the Royal Stoke University Hospital, where he remains in a serious condition.
North Wales Police are appealing for witnesses to come forward.
PC Owain Roberts from the Roads Policing Unit said: "We are particularly keen to hear from anyone who saw the red and green quad bikes prior to the collision, or who may have captured either vehicle on dashcam, CCTV, doorbell camera or mobile phone footage."
"We are especially interested in speaking to anyone who saw the red quad bike and the green quad bike travelling alongside each other in the moments leading up to the collision."
Anyone with information should contact North Wales Police on 101 or via the live web chat, quoting reference no. O115918.
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