An area around the Sydney Opera House evacuated for more three hours has reopened in the wake of authorities fixing an industrial gas leak.

About 500 people were evacuated from the Opera House forecourt area just after 3:00pm when an excavator cut a gas line, triggering the leak.

Tourists and people dining at nearby restaurants were moved away from the site, and part of Macquarie Street was closed.

An area around the Opera House was evacuated ( ABC News: Jessica Kidd )

However, after three hours of repair work with specialist equipment, the area was reopened just after 6pm.

Restaurants such as the Aria Restaurant, headed by celebrity chef Matt Moran, had been affected, with staff evacuated as they prepared for dinner service.

An Opera House spokeswoman said the Opera House building itself had not been affected and this evening's performances were expected to take place.

A state dinner hosted by NSW Premier Gladys Berejiklian for NSW Governor David Hurley is being held at the Opera House tonight.