He is described as white, in his 30s or 40s, with short dark hair and dark facial hair.
The force said he was wearing blue jeans and a dark green jacket with a white stripe on both sleeves.
Ch Insp Nick Paling, Great Yarmouth’s district commander, said: “We recognise how shocking and distressing these incidents are for the victims, their families, and the wider community.
“Specialist officers have been deployed to support both girls as we work through this investigation.”
A police cordon put in place near Great Yarmouth Pleasure Beach while inquiries were carried out has since been lifted.
Paling said there would be an increased police presence in the area as the force carried out “reassurance patrols”.
Norfolk Police has urged witnesses or anyone with information to come forward.
