The official death toll from the horrific Christchurch 6.3 magnitude earthquake has risen to 55, with another 20 unidentified bodies.

About 300 are still listed as missing, although police are working through those number to ascertain whether they are staying with friends and haven't been able to make contact.

Mayor Bob Parker revealed the latest figures and also said the city water system is "devastated".

There are still believed to be more than 100 people trapped in the PGG Building although two dozen have been rescued alive.

Police say they have received text messages from people trapped inside but that the number of texts coming through has reduced as the hours have passed.

But they are quick to point out that this is most likely to be as a result of batteries running out of power.

There are currently 200 Search and Rescue staff on the ground in Christchurch and that number will swell to 700 in the next 48 hours as reinforcements from all over the world converge on the city.

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