Fears are growing for a British backpacker still missing after jumping off a 10m-high bridge in Australia "for a bit of fun". The 30-year-old man had been drinking with four friends when the group decided to leap off William Jolly Bridge in Brisbane at about 10.30pm on 17 January.

Police say the missing man, who has not been named, was the first to jump into the water. He emerged a few seconds later but went back under the surface.

Brisbane Police 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 – the 30-year-old British national – jumped off the bridge first.

"The other three fellows said he took a running jump from three or four metres away, jumped over the rail, went under the water. He came up again a few seconds later, rolled on his side and went back under the water and hasn't been seen since."

A helicopter with infrared cameras searched up and down the river but failed to find any sign of the man. Land and water search teams had continued again local time on 18 January.

Inspector Cryer said: "We will continue our search and rescue operation until we find him. It's tragic, it's really unfortunate. Obviously jumping off a bridge into a river is a silly thing to do and we would warn against it."

The inspector added he was not aware how long the man had been in Australia, but confirmed he had been working in Brisbane and has relatives in the city. Officers say they have contacted the man's family in the UK.

Police respond to people jumping off the bridge about once a month.