BRISBANE - An Australian tugboat pilot became a local hero Thursday after he steered a runaway 300-ton concrete walkway to safety when floods turned it into a floating missile.

Churning floodwaters that swamped Brisbane ripped the massive riverside walkway, a major city landmark, free of its moorings, sending it hurtling down the river overnight towards boats, bridges and pontoons.

"We saw a very large section of the Riverwalk come around the bend. The first very large section scraped the dock... (where) there were some boats," the captain, Doug Hislop, told Brisbane's Courier-Mail newspaper.

"The second absolutely obliterated it."

But as the huge chunk of concrete threatened two bridges and key industrial sites, the plucky tug driver braved the fast-flowing water to guide it longways under bridges and past vessel moorings.

"I think everybody thinks that the 'little tug who could' made a remarkable effort," said Queensland state premier Anna Bligh, referring to a popular children's book.

"There is no doubt in my mind that the tug driver saved lives.

"Without him steering that 300-ton piece of concrete away from boats and pontoons, we would have seen that debris go into the river system and possibly into flooded areas."

Brisbane region harbourmaster Captain Richard Johnson told commercial television the tug had guided the boardwalk safely past infrastructure including chemical and fuel wharves and an oil pipeline.

"We had to start assisting it and they did an absolutely fantastic job taking it right through the centre of the Gateway Bridge without touching anything at all," he said.

Police closed the city's bridges three times overnight over fears the enormous walkway could crash into their supports.

Bligh said she would recognise the state's local heroes, including the tug driver, after the floods.

Asked whether the tug pilot would be awarded the country's highest honour, the Order of Australia, Bligh quipped: "At the very least he'll be getting a cold beer."