The level of liquefaction after Tuesday's 6.3 magnitude aftershock dwarfs the amount caused by the original earthquake that hit Christchurch in September, Mayor Bob Parker says.

Search and rescue workers have begun work in preparation for removing bodies from under piles of rubble at the Christchurch Cathedral.

A 52-year-old man is in a stable condition after having both legs amputated by a visiting surgeon at the PGC building.

Police and security staff are worrying about the possible further collapse of building facades.

Personnel at the PGC building in Christchurch have switched their focus from trying to find survivors to recovering the dead, the company says.

Rescuers have found no survivors at two Christchurch CBD buildings where signs of life were reported this morning, the Fire Service says.

The family of a woman feared dead in the earthquake has suffered another cruel blow with her home being burgled while her children waited for news.

Their task is to enter highly restricted and prohibited areas, putting their lives on the line to save others.

Hope is fading for hundreds of people missing for a second night after the Christchurch earthquake.