A quarter of the country registered for a national earthquake drill today, but despite the popularity of the exercise there are no plans to make it an annual event.

The drop, cover and hold message was practised around the country today at 9.26am today, but in Christchurch some laughed at the need to take part in an earthquake drill.

Teachers were the unsung heroes of the Christchurch earthquakes, according to a Canterbury University lecturer heading a research project.

About half of the businesses which left the Christchurch CBD after the Canterbury earthquakes are not likely to return, research has found.

Environment Canterbury is advising dust-sensitive Christchurch residents to wear dust masks as demolitions pick up in the city.

Canterbury Earthquake Recovery Minister Gerry Brownlee has backed down from comments he made about frustrated residents in damaged Christchurch homes and apologised.

The much-anticipated blueprint includes 12 key sites for major facilities, including a new 2000-capacity convention centre at a "postcard location" by the river, a huge aquatic and indoor sports facility, revitalised square with a new central library, and Ngai Tahu cultural centre. Leafy, bright "college-campus style" open space will form the compact centre of a rebuilt Garden City, designed to "solve the problem of too much land, not enough demand".

The Canterbury Earthquake Recovery Authority (Cera) in April established a central development unit, which was tasked with coming up with a blueprint for the city in 100 days. Prime Minister John Key and Earthquake Recovery Minister Gerry Brownlee released the blueprint for the rebuild of the city centre, which was devastated by last February's deadly earthquake.