Work is set to begin on a multi-million dollar fire deluge system to improve safety and reduce the risk of lengthy closures at Lyttelton Tunnel.

Transport Minister Simon Bridges says the project will also increase the resilience of a route that is an economic lifeline for Christchurch, Canterbury and the South Island.

Rock falls from the 2011 Christchurch earthquake closed the main alternative road link to Lyttelton, and since then the tunnel has provided the most direct freight access to the town and port.

A tunnel closure because of a fire could have a serious economic impact. Bridges says that once installed, the deluge system will reduce this risk and improve fire safety for tunnel users.

The $28.7 million project is the largest project undertaken at the tunnel since it opened in 1964. The contract has been awarded to McConnell Dowell, with work set to start in the coming weeks.

The project involves the construction of two reservoirs, two pump stations, and the installation of 9km of pipe work and 2,400 fire sprinkler nozzles throughout the tunnel.

Traffic disruptions will be minimal, with most work being conducted in the ducts above the tunnel, although some night-time tunnel closures and single lane operations will be required. The expected completion date is December 2018.