The Lyttelton Tunnel is closing overnight for three consecutive nights this week so its fire protection system can be tested.

The tunnel will shut at 11pm on Tuesday, Wednesday and Thursday nights, reopening at 5am the following morning each time.

The work is due to be complete by 5am on Friday 17 July.

During each closure, the tunnel will open on the hour, every hour, for about 10 minutes to clear queued traffic in both directions.

NZTA said the deluge testing was necessary to ensure the tunnel was safe for all users and met the required standards.

Motorists can still travel between Lyttelton and Christchurch via Dyers Pass Road and Governors Bay Road through Cashmere, or via Evans Pass Road and Sumner Road through Sumner, though both routes are longer than the tunnel.

NZTA thanked road users for their patience while the safety work was completed.