Tsunami sirens being installed in Rockinghorse Rd, South Brighton, in 2012.

Half a million-dollar tsunami sirens along the Christchurch coast were "a complete waste of money", Mayor Lianne Dalziel says.

A city council committee has approved a Civil Defence Emergency Management implementation plan after a review found residents were "bombarded" and confused by mixed messages during a tsunami evacuation after the magnitude-7.8 earthquake on November 14.

The review, commissioned after criticism about the emergency response, found coastal residents waiting for tsunami sirens after local earthquakes were putting themselves at "significant risk".

GEORGE HEARD/STUFF Christchurch Mayor Lianne Dalziel is not a fan of the city's tsunami sirens.

The plan puts the review recommendations, such as educating residents on evacuating without relying on sirens, in place. The report did not make recommendations on the sirens' future.

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Dalziel said on Tuesday the sirens were "a complete waste of money, particularly in the Christchurch coastal environment".

This was because of the likely nature of tsunami threats in the city and "the fact they are only sirens and don't provide for voice commands".

The report identified three tsunami scenarios for Christchurch.

A regional tsunami, which had approximately one to two hours of warning time, and a distance tsunami, with 10 to 12 hours of warning time, were the most common.

That meant there was time to send evacuation messages on platforms other than sirens.

A local-source tsunami, which was less common, occurred within one hour of the triggering event. When the sirens were installed in 2012, the council said there would not be sufficient time for the sirens to be activated for a local tsunami.

On November 14, the sirens were not activated until a national warning message was issued by Ministry of Civil Defence and Emergency Management (MCDEM) at 2.01am, two hours after the local earthquake.

MCDEM did not recommend using tsunami sirens for local-source tsunamis, especially those without voice capability.

"The siren's a waste of time unless it was sounded as an all-clear and there's no differentiation," Dalziel said.

Members of the Strategic Capability Committee agreed to request another report on tsunami siren options that would include information on tsunami risks.

In 2012, during Sir Bob Parker's mayoralty, the city council installed 22 tsunami sirens on the coastline between Waimairi Beach and Sumner at a cost of $550,000.

About $120,000 was funded by Eaton Industries Company.

The sirens were to be used to signal evacuations of Christchurch's coastal area in the event of a distance tsunami and possibly a regional tsunami, if time permitted.

"With a distant earthquake, we would get 12 to 15 hours notice and there are evacuation plans in place," Parker said at the time.