Christchurch City Council is installing sirens along nearly 11km of the coast to warn of incoming tsunamis.
Aftershocks have rattled the city since just before Christmas.
Mayor Bob Parker says the risk of a large tsunami from one of the faultlines off the coast of Christchurch is extremely small and the main threat comes from earthquakes in South America.
He says 47 sirens will be installed from Waimairi Beach in the north to Sumner in the south.
