A new climbing robot is revolutionising the way inspections are carried out inside 7.2 kilometres of hidden tunnels in the arches of the Sydney Harbour Bridge.

University of Technology Sydney (UTS) engineers and Roads and Maritime Services (RMS) have spent five years developing the robot, which has magnetic feet and can scale the complex passageways deemed too dangerous for human workers.

The robot applies a three-dimensional sensor to create a map of the dark tunnels, and then moves through the space — climbing up and down walls and through small passages.

It sends back real-time information to engineers above who can use a camera to assess any damage.

Bridge inspector Laurent Matkovic said the process made things safer for the workers.

"It's better to send a machine into a confined space than myself, because if something happened to me I would be blocked inside," Mr Matkovic said.

RMS manager for strategic infrastructure Peter Mann said the vast network of confined spaces included regular drop-offs of 1.5 metres.

Workers enter through 30-centimetre hatches every six metres along the span of the bridge.

The prospect of rescuing a crew member who might become trapped inside is a sobering thought — given the openings are too small to accommodate a stretcher.

"There's risk of asphyxiation. Air quality is an issue inside the arch," Mr Mann said.

"Also emergency rescue is a real problem for us. These days we'd prefer to send robots in to do the dangerous jobs."

Plan for robot that can vaporise rust using laser beams

A University of Technology Sydney engineer near the summit of the Sydney Harbour Bridge inspects the live map being created by the robot in the tunnel below. ( ABC News: Nicole Chettle )

ABC News visited a section of the bridge with the engineers, where one section was opened for the first time in five years.

The paintwork inside this part of the bridge dates back to 1932.

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The engineers said the next stage of this project would be developing a robot that could inspect the area, vaporise rust using laser beams, and re-paint the section at the same time.

Mr Mann said traditional sandblasters were not suited to the job because they created a lot of dust in a confined space.

He said it was hoped the new machine would include a vacuum to remove waste, and be nimble enough to complete the job without sending workers in wearing special gear to protect them from noxious gas and dust.

One of the UTS engineers involved in the project, Peter Ward, said this world-first development could have important applications overseas.

"I can see this on other structures like transmission towers, ship hulls and nuclear reactors," Mr Ward said.

"Other places where you don't want to send people and it's too difficult to access."

The robot has already won an international technology award in Sri Lanka and an Australian work safety prize.

The next version, complete with lasers, is planned to be ready in three years.