Man rescued after houseboat sinks as Brisbane River rises in south-east Queensland flooding

Onlookers gasp in horror as houseboat submerges after collision with ferry dock in Brisbane.

A man has been pulled from the flooded Brisbane River alive after a houseboat sank in the extreme weather lashing south-east Queensland.

Dramatic footage taken by onlookers on Sunday morning shows the houseboat gaining speed as it floats towards a Kangaroo Point ferry terminal.

The vision shows the boat rapidly sinking as soon as it collides with the terminal.

A person was seen in the water as the boat flipped over and floated away.

Horrified onlookers called Queensland Police. A spokesman confirmed police were on the scene shortly before 9am.

Follow our rolling coverage of south-east Queensland's severe weather event in the live blog

An eyewitness told ABC Radio Brisbane a tugboat also responded quickly to the stricken houseboat.

The man in his 70s was pulled from a pontoon at the nearby Howard Smith Wharves by workers and volunteers.

The man was pulled to safety at Howard Smith Wharves. (Supplied: Matthew Toomey)

Matthew Toomey said he was walking past the Howard Smith Wharves ferry terminal about 8:40am when he saw several staff from the nearby brewery rush to the edge of the raging Brisbane River.

He said they worked for more than 10 minutes to rescue the man, using a pole and at one point forming a human chain in an effort to lift debris off him before pulling him from the water.

People are seen linking arms to help rescue the man from the pontoon. (Supplied: Matthew Toomey)

"He was certainly under something because they were trying to lift the boat or pontoon, one of those things, there was definitely something on top of him," he said.

"Obviously, they [the rescuers] didn't want to go into the water themselves because they just get swept away."

Mr Toomey said the water in the river was "incredibly fast moving" and while a police boat was nearby in the river, officers could not make it to shore or keep the vessel steady to offer assistance.

"Where he was and to be trapped under something, he could have easily been trapped deeper under the water and drowned," Mr Toomey said.

"He looked pretty shocked getting out because I'm sure a lot would have gone through his head."

Mr Toomey said police and ambulance arrived at the scene to offer treatment shortly after he was retrieved from the water, adding that the rescued man was able to walk following the ordeal.

A Queensland Police spokesperson confirmed the man was the only occupant of the houseboat when it sunk and that he jumped from the boat into the river.

They said he suffered no significant injuries.

The dramatic rescue came amid widespread flooding across south-east Queensland and the north of New South Wales.