More aftershocks at Christchurch

Christchurch will reopen on Tuesday, but people are warned to be cautious as aftershocks continue.

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A LARGE part of central Christchurch will reopen to businesses and the public on Tuesday morning, but authorities are warning people to be cautious as aftershocks from Saturday's devastating earthquake continue.

Civil Defence warned that the area could hit by another big aftershock after residents were kept awake overnight by a series of strong aftershocks.

The aftershocks, ranging from 3.1 and 5.4, that shook the city overnight meant the inner-city cordon that had kept the public out of the city centre could not be reduced to the extent initially planned, Christchurch City Council rescue manager John Buchan said.

But they would be relaxed at 8am (0600 AEST), with Cathedral Square and Colombo Street reopening.

"This is a major step toward freeing access to the city," Buchan said.

There would be full access for building owners and the public in this area, except where damaged and unsafe buildings had been taped off.

"We do however urge that people exercise caution as aftershocks continue," Buchan said.

The aftershocks included one with a magnitude of 5.2 shortly before 11.30pm, one of 5.4 soon after, and another of 5.4 at about 3.30am on Tuesday.

The council said its staff, the Fire Service and Urban Search and Rescue had dealt with thousands of calls about houses and assisted homeowners with securing their houses, removing chimneys and ensuring access to properties.

All 678 buildings in the CBD were inspected and buildings were affixed with either a green, yellow or red placard. Green means safe, yellow means limited access and red means the building is unsafe. Sixty nine per cent of buildings have a green placard, 26 per cent a yellow and five per cent a red.

Civil Defence said less than five per cent of city properties were without water.

Staff repaired 100 leaking water pipes, returning water to 21 streets, with it still cut off for 38 streets.

Fewer than 1000 power customers remain without power.

Bus services are resuming on Tuesday morning, with the exception of the inner city shuttle, while most schools are expected to reopen on Wednesday.

About 250 people stayed in welfare centres overnight.

The aftershocks kept the region tense on Monday, as people came to terms with the destruction, with the government estimating 100,000 homes were damaged.

A street in suburban Bexley was evacuated yesterday because the sections were covered in deep layers of silt.

There were health concerns too, with two families in a welfare centre reported to have contracted gastroenteritis, though it was not known whether they had caught the stomach bug before the quake or after it.

But health authorities reinforced the message that people should continue to boil drinking water for at least three minutes.

New Zealand Prime Minister John Key will travel to Christchurch on Tuesday afternoon to meet the region's mayors and inspect damage.

He said on Monday the government was paying $NZ5 million ($A3.9 million) in to the mayoral relief fund, to help those suffering hardship. The Warehouse, BNZ, Westpac, Fonterra and Fletcher Building promised $NZ1 million ($A700,000) each towards flood relief efforts.

The Earthquake Commission has received 15,000 claims already.