A time frame's been put on the expected length of rescue operations at some of Christchurch's worst-affected buildings.

Teams from across globe touched by city's loss toil side by side amidst rubble.

Strong winds that were set to hit Christchurch this afternoon did not eventuate, but residents are warned that they should secure loose roofs and beware of the threat of falling masonry.

As the Government commits itself to rebuilding earthquake-ravaged Christchurch, it is looking at costs running into tens of billions with an economic impact that will last for years.

Specialised search teams tunnel through the darkness to find survivors of the quake.

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.

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

Police have delayed releasing the names of those confirmed dead and for whom there are serious concerns.

There is no possibility of survivors in the rubble of the Christchurch Cathedral, police said this afternoon.

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.