Police have released four more names of victims of the February 22 Christchurch earthquake.

They are:

* Siwen Huo, 28, of China;

* Kayo Kanamaru, 19, of Japan;

* Erica Avir Reyes Nora, 20, of the Philippines; and

* Caiying Ye, 27, of China.

One hundred and sixty-six people are confirmed dead following the magnitude 6.3 quake but police believe the final toll will be 180.

Police have released the names of 117 victims.

Earlier today Civil Defence Minister John Carter extended the state of national emergency for a further seven days.

A state of national emergency was first declared on February 23, and extended on March 1 and March 7.

It is expected to continue for several more weeks, Mr Carter said.

"Continuing this declaration means the National Controller remains in control of the functions, duties, and powers of the Civil Defence emergency management groups and group controller. He works in consultation with central government and local authorities, including the mayor, on this massive recovery operation," Mr Carter said.

"It has been nearly three weeks since the earthquake and I am constantly impressed by the willingness of everyone involved in putting Christchurch back together to pull out all stops to ensure people's most urgent needs are met as quickly as they can be."

Under the Civil Defence Emergency Management Act 2002, a state of national emergency can be declared for a maximum of seven days at a time only.

Thousands expected to return

Thousands of people are potentially expected to return to Christchurch in coming weeks, Civil Defence national controller John Hamilton says.

Most of those returning would be due to the fact that 110 schools will reopen tomorrow, rising to 143 by the end of the week - or 88 per cent of schools in Christchurch.

"In addition, by the end of the week 234 early childhood education centres will be open," he said.

This would raise issues around power and water services, he said.

Mr Hamilton said the sewerage system in Christchurch was still fragile and authorities are not sure how they will cope if it rains.

The shortage of portable toilets in the city had been largely remedied by the arrival of another 960 from the United States on Saturday.

"Another 200 will arrive on Tuesday and both lots will be assembled and distributed to the suburbs as soon as possible," Mr Hamilton said.

The suburbs of Avondale, Bromley and Avonside would benefit first from the arrival of another shipment of chemical toilets, boosting the total number to 19,000.

Rob Jamieson of Orion says just 550 customers remain without power in Christchurch outside the CBD.

Access for business owners

Business owners from two of the restricted areas of the central business district (CBD), Zone Four and the Red Zone, would be allowed controlled access to their properties to recover essential items, Mr Hamilton said.

However, he warned that access would return to "zilch" after the recovery time was up. All business owners eligible to re-enter their premises have been contacted.

"We understand business owners will want to retrieve key items but urge them to be patient with us as we work through this complex process," he said, adding that some businesses owners would not be admitted because of safety reasons.