The Briton, who was with a group of friends, is understood to have leapt into the water in Brisbane “for a bit of fun”, and “to cool down”, Sky News said.

Police have been searching the banks of the Brisbane River after the man decided to jump off the William Jolly Bridge, after drinking at a backpacker’s hostel on Sunday night, police said.

Inspector Sean Cryer said: "They had agreed between themselves that they were going to jump off the bridge for a bit of fun and to cool down.

"The young man in question, a 30-year-old British national, jumped off the bridge first."

Cryer added that the Briton had come “back up again a few seconds later, rolled on his side, went back under the water and hasn’t been seen since."

The man’s companions reportedly alerted emergency services after failing to find him and a helicopter was called in to scour the river but without result.

The missing man was not named, but his family are understood to have been contacted.

"I think you would probably find that people have been jumping off that bridge since they built it. Sometimes they live and sometimes they die," Cryer added.