A man has been taken to hospital after being dragged out of the Brisbane River early this morning.

The man, believed to be in his 20s, was seen struggling in the water at South Bank about 5.00am.

Chris Wright was jogging nearby and says a security officer alerted police.

"Lucky for the workman in the high-vis outfit who pointed out there was somebody in the river, [otherwise] he might have drowned before anyone could see him," Ms Wright said.

"So it was a good effort all round, firstly by the workman and by the police.

"The police officer without hesitation just stripped off his boots, scrambled down the rocks and went straight into the river without a moment's hesitation.

"It appears like [the man] is in shock but he can move.

"But it seems he doesn't have a very good command of English."