One of the tallest buildings in Christchurch, The Grand Chancellor hotel, is on the brink of collapse following yesterday's devastating earthquake.

As another significant aftershock hits Christchurch, emergency services are being pulled back from the building for safety reasons.

The 26-storey hotel has slumped in one corner and there are fears it will fall. One floor inside has already collapsed.

In the last 10 minutes The Grand Chancellor hotel has moved about a metre horizontally and is now on a lean to the east.

Should the hotel come down, it will destroy other buildings in the central city.

Fire Service national commander Mike Hall said search and rescue teams had moved away from the Hotel Grand Chancellor half an hour ago on the advice of engineers who said it was on the verge of collapsing.

Police and firefighters cleared a two-block exclusion zone around the Grand Chancellor Hotel, forcing a halt to rescue work on some of the buildings smashed in yesterday's 6.3-magnitude earthquake.

The tremblor struck at 12.51pm, 20km southeast of Christchurch at a depth of 5km. There have been dozens of aftershocks, and power and water has been cut to large areas of the city. New Zealand declared a national state of emergency Wednesday after the quake left nearly 400 people dead or missing.