A search is underway in the Brisbane River for a 44-year-old man reported missing at Yeronga, in Brisbane's south-west, on Saturday afternoon.

The man is believed to have entered the water at the Somerville House Water Sports Centre on Brisbane Corso to retrieve a remote-controlled toy boat.

He got into difficulties with the strong Brisbane River currents and was swept downstream.

The man's partner followed him along the riverbank for about 200 metres before she lost sight of him and alerted Queensland Police.

Acting Inspector Andrew Dupere said a search and rescue mission is underway involving the police helicopter, swift-water rescue teams, ambulance and State Emergency Services.

"We were called here at about 4:00pm in relation to a male that's gone into the water to retrieve a toy, a remote-control toy, and as a result, he's been swept downstream," he said.

"The current was flowing pretty fast and he's gone downstream pretty quickly.

"We always err on the positive side so we're hopeful that we can locate this male clinging to the side.

"There are a lot of mangroves here so we're hopeful we can find him alive."

Acting Inspector Dupere said the search would continue until about midnight and resume at first light on Sunday.

In the meantime, police are asking the public to report any sightings of a man climbing out of the Brisbane River in the Yeronga region.