Blackwatch Pass was closed to traffic yesterday as work to shore up its walls started.

A government spokeswoman said work will continue for “several weeks”.

Workers on the project will remove areas of soft rock and vegetation and secure weaker sections of the pass. The link from North Shore Road to Hamilton, with an overpass leading to Government House, opened in 1934, and has been subject to falling rocks in the past.

Plant roots can bring down rubble as can weathering of exposed rock.

Similar work on the rock face was carried out last April.