A man has been badly mauled by a shark at the popular Rottnest Island holiday spot of Geordie Bay.

The critically-injured victim, understood to be in his 30s, was brought out of the water and onto a wooden jetty, where paramedics attempted to save him.

Police were also at the scene, with a water police vessel moored nearby.

7NEWS vision showed a dozen people were huddled around the wounded man, who was partly covered by a blue blanket.

Emergency services were scrambled just before 10am. An RAC Rescue helicopter was sent to the incident.

WA Police said it was advised of a possible shark attack off Geordie Bay at 9.55am.

“A male person is believed to have been bitten by a shark and is being conveyed by boat to shore and will be met by SJA WA paramedics,” a spokesperson said.

The Department of Primary Industries and Regional Development said it was alerted to the shark attack at 9.54am.

“DPIRD is working with local authorities, and further information will be provided as it becomes available,” a spokesperson said.

It urged the public on the island to take additional caution in the Geordie Bay area.

More to come.