Changes to tsunami alert warnings are being rolled out in Christchurch, after mixed messages caused confusion during the November earthquake.

A review by the Christchurch City Council reveals coastal residents didn't know when to evacuate to or where they were meant to go after the 7.8 magnitude quake hit the region.

New plans will target inconsistent messages by clarifying who is in charge and where people can find safety.

Christchurch City Councillor David East says sirens didn't go off until more than an hour after the last earthquake - something that shouldn't happen again.

"Time is critical - any effects of the tsunami would have well been and gone by the time they turned the alarms on."

Christchurch East MP Poto Williams said the changes are good, but people should always rely on their instincts if they feel unsafe.

"There were lots of people that I spoke to that morning saying 'we're not going to wait for the sirens, we're going now'."

"People's basic instincts are appropriate and they should, if there is any doubt, go."