The incident came as rescuers were combing a waterway near Gympie for another man who was swept away in floodwater on Monday evening while his wife watched.

Paramedics rushed to Norman Creek, Woolloongabba, about 6.35am after a passerby found the pedestrian and the car in the creek, just off Turbo Drive.

The pedestrian, believed to be in his 40s, was rushed to the Princess Alexandra Hospital in a critical condition with significant chest and pelvic injuries plus signs of "post-immersion", a Queensland Ambulance Service spokeswoman said.

She said the driver of the car, also a man, managed to get himself out and was taken to the same hospital in a stable condition.

Overnight, Queensland Fire and Emergency Service crews searched Marys Creek, near Gympie, for more than six hours after a man was swept away in floodwater.

A 67-year-old man and his wife both got out of their car after it went into the water at Marys Creek Road, Marys Creek, about 6.50pm on Wednesday, according to police.

But police said the man re-entered his car to try to remove it from the causeway and the car was swept away.

The search resumed at first light and the car was found about 7.25am but police were yet to confirm whether or not the man was inside.

"We had several swiftwater crews out here operating for over six hours, walking the banks, under really difficult conditions," QFES swiftwater crew member Peter Watson told Nine News.

" ... We've conducted a search probably six kilometres, eight kilometres up and down the river and we're back here in better light today.

"It was getting a bit dangerous last night and ineffective to do it thoroughly."

Further north in Mount Tom, between Miriam Vale and Agnes Water, swiftwater rescue crews were called to reports a person was stuck on the roof of a submerged car.

Rescuers was out there by 6.15am but a Queensland Fire and Emergency Service spokesman said they were still yet to reach the car.