Wellington: Three hundred people are missing and 75 bodies have been recovered from the quake ravaged New Zealand city of Christchurch, local authorities said on Wednesday.

Christchurch Mayor Bob Parker said there were now 55 identified bodies at a morgue, which had been set up at local military base. Another 20 bodies had been recovered, but were not yet at the morgue and had yet to be identified.

Parker said it was hoped that many of those 300 missing people would be accounted for over the course of the day.

Search and rescue staff also said many people remain trapped alive inside buildings destroyed by the 6.3-magnitude earthquake on Tuesday afternoon.

More than 120 people had already been pulled from collapsed buildings as rescuers worked through the night under floodlights in the rain.

Search efforts are concentrating around 10 buildings, where it is feared more than 100 people could still be trapped. These included a number of Japanese students who had been studying English in Christchurch.

Fifteen people were confirmed alive in one building as rescuers tried to get to them as quickly as possible through tonnes of rubble.

Earlier police said they were having to leave bodies as they concentrated on getting to survivors, some of whom had to have limbs amputated to get them out of rubble.

Prime Minister John Key said on Tuesday night that New Zealand faced one of its darkest days.

Key held an emergency cabinet meeting on Wednesday and pledged all assistance possible to Christchurch in both the initial aftermath and the long rebuilding programme ahead. He thanked the international community for assistance.

More than 200 patients have been admitted to Christchurch Hospital's emergency department with many more treated at emergency medical stations around the city.

Injuries range from minor cuts to serious spinal injuries with some patients airlifted to Auckland 1,000 km away.

There were now more than 200 search and rescue staff working through the city with another 500 joining them over the next two days as international offers for assistance come in. More than 1,000 armed forces have also been deployed to assist.

The quake struck on Tuesday at 12.51 p.m. when office buildings and streets were full of people.

The quake was much shallower and nearer to the city than the 7.1 quake that caused widespread damage in September but resulted in no deaths.

Buildings that stood up to last year's event, including an historic cathedral, collapsed this time.

Electricity, water, sewer and gas lines were disrupted by the quake with fires breaking out in the city overnight.

Most of the city has no water supply and all schools and most businesses were closed with people being urged to stay at home and consider leaving the Christchurch area if possible.

Communication with the area was difficult with phone systems disrupted and there have been appeals for people to stop using mobile phones throughout New Zealand.

Christchurch is New Zealand's second-largest city and home to around 370,000 people.

The quake was felt throughout New Zealand and caused 30 million tonnes of ice to break off from the Tasman Glacier, about 200 km away.