The Sydney Opera House has been in operation for 37 years, but the NSW government insists that the cranking of the stage machinery is not a safety risk.

An engineering report done by theatre consultants Marshall Day Entertech said that there may be possible "multiple fatalities" if a serious malfunction will occur.

The Opera House would need to be closed unless repairs that would cost $800 million were done, Sydney's Daily Telegraph reported. However, the NSW government played down the risks and expenses.

Director-general of Communities NSW Carol Mills said that the Marshall Day report was included in the needs-and-costs assessment of arts organisations. It did not estimate the risk of accident but focused on potential problems.

Even though the stage machinery was "nearing the end of its life", Ms Mills said that the Opera House employees had "never been safer".

The management of the Sydney Opera House said that the cost for repairs was heightened. The $800m that was quoted was for the total refurbishment of the Opera Theatre according to architect Joern Uzon's design. The cost for the upgrade of the stage machinery alone would be about $50m.

According to Opera House chief executive Richard Evans, any of the venue's theatres is not up for closure.

"Sydney Opera House has a $30m annual plant and equipment maintenance program, widely acknowledged as one of the best in the world," Mr Evans said.

Discussions for the upgrade of the Opera House have went on for years and malfunctions have occurred.

"Some time in the next five years, we will have to close for a period for repairs," Opera Australia chief executive Adrian Collette said.