The man, who has a large build, was seen entering the river at Macquarie Street, St Lucia, about 4am on Tuesday, Queensland Police said.

Officers started searching the riverbank while swift-water rescue crews began looking for the man in the water.

“Anyone who may have observed a man in the river is asked to contact police immediately,” police said in a statement on Tuesday.

Police are still trying to identify the man and have also asked residents or businesses in the Macquarie Street area to check CCTV cameras for any footage of him.