Grieving New Zealanders held church services for victims of the deadly Christchurch earthquake Sunday as the danger of falling debris frustrated efforts to recover bodies.

Only one body was pulled from the rubble overnight, bringing the death toll to 146, but police warned "we continue to believe that there are more than 200 people missing in the worst damaged parts of the city".

With the number of fatalities from Tuesday's 6.3-magnitude quake steadily rising, Prime Minister John Key has warned the disaster "may be New Zealand's single most tragic event", outstripping a 1931 quake which killed 256.

Police superintendent Russell Gibson said rescuers knew where bodies were located but could not reach them as ruined buildings in the disaster zone teetered on the brink of collapse.

"I know that they (rescuers) can see bodies that they're trying to get out, it's tragic," he told Radio New Zealand.

Office blocks folded like packs of cards as the quake toppled entire shop frontages, tore up roads and opened huge fissures in the ground, leaving one third of the downtown area facing demolition.

No survivors have been found since Wednesday afternoon but Gibson said international rescue teams working on the worst-hit buildings insisted there was still hope.

"The commanders there, one from Great Britain and the other from Australia, were saying 'look 10 days, it's not unusual to get down and find people alive', so we're positive," he said.

More rescue specialists from Thailand and Britain were due in the city Sunday to relieve fatigued colleagues who have been working around the clock on the grim task of scouring the debris.

The city's landmark cathedral lost its spire in the quake, entombing up to 22 people in the ruins and forcing worshippers to gather at a nearby chapel Sunday.

Anglican archbishop of Christchurch Victoria Matthews, who would normally lead Sunday prayers in the cathedral, said she wanted the quake-scarred city of 390,000 to begin the healing.

"Don't deny your grief, don't pretend that you're not traumatised," she said.

"Accept that you have gone through some of the hardest days of your entire life but also accept that there's healing and fullness if you will work towards it," she told Radio New Zealand.

But there was also anger in New Zealand's second largest city after a spate of looting and burglaries in the wake of the disaster. Police said one man was arrested for theft overnight.

The St John ambulance service said the latest problem was hoax callers wasting its time and resources.

"The ugly side of human nature is being revealed with hoax calls about people injured and trapped in buildings by the Canterbury earthquake," spokesman Nicky Green said.

"It's really sad because it's wasting everyone's time."

Scores of foreigners are among the dead and missing, many of them Asian students who were attending a language school housed in an office building that was reduced to smouldering ruins.

Police said they were making "significant progress" combing through the wreckage of the building and Tertiary Education Minister Steven Joyce was due to meet representatives of the language school later Sunday.

Citizens from Japan, China, the Philippines, Thailand and Korea are among more than 60 students and staff from the school who remain unaccounted for.

Meanwhile, residents struggling to cope without power, water and sewerage facilities in large parts of the city were warned of a new danger from falling rocks in the city's hills dislodged in Tuesday's seismic jolt.

More than 20 homes were evacuated in the suburb of Mount Pleasant because their houses could be in the path of boulders.