The 16-year-old was one of a group of four who went into the water around 8pm on Monday at Scarborough Beach.

He has not been found during an extensive land and marine search.

"We believe that the chances of survival for this long is unlikely," Acting Inspector Cindy Morgan told reporters on Tuesday.

"This is a tragic incident and we are going to support everyone involved, including family, friends and witnesses."

Acting Insp Morgan said witnesses had rushed into the water to pull at least one of the other three youths out of the water.

"Whether or not it was a rip that took them out or they were hit by a wave is unknown to us at this stage," she said.

"We believe that he was an inexperienced swimmer and obviously that makes it difficult to keep your head above water."

Devastated family members were seen scaling the beach with torches overnight as they desperately tried to find the boy.

Police believe his mother is currently in Ethiopia.

Authorities began an air, sea and land search for the boy that continued late into the night.

Six vessels from Water Police and Volunteer Marine Rescue supported by Rescue 651 searched the ocean as police and surf lifesaving personnel patrolled the beach.

The search effort resumed at first light on Tuesday, but Acting Insp Morgan said it would be scaled back to a recovery mission.

Australian Associated Press