Options for rebuilding Christchurch Cathedral may have narrowed after Monday's powerful earthquakes caused further serious damage to the iconic building.

The damaged cathedral lost its celebrated stained-glass Rose Window and more of its structure on Monday when a 5.7-magnitude quake was followed by a 6.3-magnitude shock.

The 19th century building had already partially collapsed and had lost its tower as a result of the February 22 quake, which also measured magnitude 6.3, and claimed 181 lives in Christchurch.

After the February 22 quake, it was feared that up to 22 people might lie dead under fallen debris in the cathedral, but the fears proved unfounded and the death toll turned out to be zero.

"The Rose Window has now completely come down and about 75 per cent of the west wall has now come down, so it's pretty sad," cathedral dean Peter Beck said yesterday.

"And we anticipate that obviously more structural damage has happened to the building as a result of the quakes [on Monday]."

Options ranged from rebuilding the cathedral as it was to "a completely different building".

Despite the latest setback, plans to enter the cathedral to recover precious items such as the organ would go ahead if it could be done safely, Mr Beck said.

Rebuilding options would continue to be explored by a specially formed project group "because we will be rebuilding in some form or another".

"It takes a long time to get the kind of structural analysis you need to make the kind of decisions we have to make. There's lots of things we don't know.

"At this stage it's too early to say which parts of the building can be retained and which parts of it will need to be taken down."

Mr Beck said no plans for the cathedral would go ahead without it being safe to do so.

The building stood up "remarkably".

"No one lost their life there. And no one was severely injured there. And that's a testament to those who did the earthquake strengthening over a decade ago."

The setback for the cathedral is only the latest for Christchurch's landmarks.

The time ball station at Lyttelton, which was damaged in the February quake, was completely destroyed on Monday.

The hotel Grand Chancellor, which was scheduled for demolition, also suffered further damaged and now has a greater lean.

And Christchurch's Cathedral of the Blessed Sacrament suffered substantial damage in Monday's quakes also.

Christchurch Cathedral
Rose Window destroyed. Chances of rebuilding narrow.

Time ball station, Lyttelton
Completely destroyed in Monday's quake.

Hotel Grand Chancellor
Scheduled for demolition, further damage on Monday.

Cathedral of Blessed Sacrament
Substantial damage on Monday. Inspections being carried out.