Tsunami sirens installed along the coast in Christchurch were being tested for the first time.
Sirens were scheduled sound for about two minutes at 11am on Sunday.
Christchurch City Council civil defence manager Murray Sinclair says the sound can be heard up to 600 metres inland. The sirens should be audible from Waimairi Beach to Sumner.
The warning system is designed to alert people of a distant source tsunami, which would take about 12 hours to reach New Zealand. The most likely cause would be an earthquake near South America.
Mr Sinclair says the test provides a good opportunity for people to think about a plan for an emergency.
"What they might need to do, where they're going to go, who they're going to look after - any elderly relatives or someone who might need assistance to get out."
He says residents should have a plan in place to leave by bicycle or on foot during an emergency, to avoid traffic congestion.
Residents are not required to evacuate during the test.
The sirens will be tested twice a year, when daylight saving begins and ends.