Workers have begun working on a one-year project to repair the earthquake- damaged New Brighton Pier in Christchurch.

The pier was damaged in the 2011 earthquakes, and repairs will mainly be to the support columns.

Most of the work will be going on below sea-level.

The cosmetic damage on the deck and railings will also be worked on.

Fulton Hogan will be under taking the repairs and it's expected the pier will re-open on Feburary 13, 2018. The work is expected to cost $9.7 million.

Some of the support columns are vulnerable to rust from the damage.

"The faster we fix them, the less chance there is for them to deteriorate in the marine environment.

This work is essential if the pier is to have a long lifespan," says David Adamson, Christchurch City Council's general manager of city services.

The work below sea level will be done inside caissons, which are segmented watertight tubes.

""I'm told it's a bit unnerving when you're standing under all that water, but the caissons create a safe, dry space in which to work. It's also the fastest option."

The pier will stay open for use while the work is going on, and the council says there will be minimal impact to visitors, other than the closing occasionally to let contractors in and out.

Popular events based around New Brighton Pier will all go ahead as planned throughout 2017.