A $28.7 million upgrade of the Lyttelton Tunnel will take place over the next 18 months, improving safety and reducing the risk of a lengthy closure.

The fire deluge system to be installed represents the largest work undertaken on the tunnel since it opened in 1964.

The system will effectively manage a fire until fire services can reach the scene, Transport Minister Simon Bridges says.

A tunnel closure would have a serious economic impact on the lower part of the South Island, he said.

"In addition to improving safety, 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.

"Since then the tunnel has provided the most direct freight access to the town and port."

Work by contractors McConnell Dowell will start in the coming weeks.

Two reservoirs, two pump stations, 9km of pipe work and 2400 sprinkler nozzles are to be installed.

Some night-time closures will take place during the work, along with occasional single-lane operations but Mr Bridges said there would be minimal disruption to traffic.

NZ Newswire

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