The Lyttelton Tunnel will close overnight for three nights next week for testing of its fire safety systems.

An NZ Transport Agency spokesperson said the State Highway 74 tunnel would be closed from Tuesday 14 July to Thursday 16 July, between 11pm and 5am each night.

The closures are needed for deluge testing, which checks the tunnel’s fire protection system.

NZTA said the tunnel would open on the hour to clear queued traffic.

Motorists are being asked to plan ahead and allow extra time. People travelling between Christchurch and Lyttelton can use Cashmere, Dyers Pass Road and Governors Bay Road, or travel via Sumner, Evans Pass Road and Sumner Road.

The agency said the Sumner route was the longer of the two detours.

“Thank you for your patience and understanding while these essential works take place,” NZTA said.