New modelling shows fewer properties would need to be evacuated if a tsunami hit the Selwyn district.

The district’s tsunami evacuation zone around Te Waihora/Lake Ellesmere has been reduced, with the old red and orange zones replaced with one blue evacuation zone.

The boundary now more closely follows areas which could be flooded or isolated in a rare, large tsunami.

The updated map, which can be used to search for individual properties, is part of a national shift to a single blue evacuation zone across New Zealand by 2031.

If you are outside the blue tsunami evacuation zone, you do not need to evacuate. If you live in the blue zone and feel an earthquake move inland to a place outside the tsunami evacuation zone as soon as the shaking stops. Photo: Supplied

Selwyn District Council head of emergency management Al Lawn said the change would make evacuation advice easier to understand.

“One blue zone means people no longer need to work out if they need to follow the advice for the red zone or the orange zone.

“Now it’s simpler — if you are in the blue zone and feel an earthquake that is more than a minute long, or it’s strong, making it hard to stand, get gone,” Lawn said.

Al Lawn. Photo: Supplied

The former red, orange and yellow tsunami evacuation zones in Christchurch were also replaced this week with a single blue evacuation zone. You can check the updated zones at Christchurch City Council.govt.nz/tsunami.

The city's network of tsunami warning sirens are also being removed in conjunction with the zone changes after Christchurch City Council opted to use Emergency Mobile Alerts as the primary warning method.

City council head of civil defence and emergency management Brenden Winder said in a statement last week the move to a single evacuation zone would make it easier for people to know when to act during an evacuation.

“The new blue tsunami evacuation zone provides a simpler and more consistent approach that will help people make quicker decisions.

“If you’re in the blue tsunami evacuation zone and you feel a long or strong earthquake evacuate immediately.

“Don’t wait for an official warning, you should move immediately inland or to higher ground,” Winder said.

Lawn also reminded people to have an evacuation plan in place and an emergency kit at home.

“Evacuate out of the blue zone. Do not wait for an official warning. If you are outside the blue zone, stay where you are. Unnecessary evacuation can delay people who need to leave.”

Lawn says “it is up to you to be ready” for a disaster.

“For everyone, especially in the blue zone, we need to remember emergencies can happen at any time.”