People who force their way through cordons into Christchurch's quake-ravaged central business district (CBD) could be killed, police say.

Central Christchurch business owners stormed through a cordon this afternoon as a protest about their treatment by earthquake authorities became heated.

"The CBD is a very dangerous environment... They're putting their own lives at risk when they actually go within the cordoned area," Christchurch Superintendent Andy McGregor said.

Some buildings were still unstable and in danger of falling, especially if large aftershocks continued to strike.

About 100 CBD business owners were at the protest, which began calmly at 2pm.

The protestors marched to the Civil Defence headquarters at the Christchurch Art Gallery, holding signs and shouting for answers about the fate of their businesses.

"Quakes didn't destroy us, council did," one protestor yelled.

Protestors called for Civil Defence national controller John Hamilton, but when he did not appear some stormed through the inner city cordon.

A soldier, unable to stop the group, simply asked them to be careful.

Some protestors ran down streets, with police in pursuit on bicycles.

Most protestors were escorted back outside the cordon, with protestors yelling "that's criminal" when one man was wrestled to the ground by police.

The protestors then stood outside the cordon to continue their protest, with a line of police officers blocking them from going any further.

Mr McGregor said he understood why business owners were so frustrated but storming the cordon was not the answer.

"It has actually got to be done in quite a structured, systemic way. We can't just have people going in when they feel like going in," he told Radio New Zealand.

Meanwhile, a three-day moratorium on demolition work in Christchurch's CBD, which was due to end tomorrow, may now be extended.

In the CBD, Civil Defence had approved 139 buildings for demolition, deconstruction or dismantling.

From Tuesday, Civil Defence planned to allow business owners controlled access to buildings within the CBD's red zone, to enable them to retrieve essential items for operating at other sites, National controller John Hamilton said.

Access was likely to be arranged building by building for small groups at a time, accompanied by engineers and Urban Search and Rescue crew for safety.

Water has been restored to almost all Christchurch properties outside the red zone.

Anyone without water should call Christchurch City Council as soon as possible if their neighbours were also without water, Civil Defence said.

However, if their house was the only property without water they would need to call a plumber and the Earthquake Commission could help with grants of up to $2000.

Water testers were taking samples from homes to test for contamination.

People still needed to boil water until further notice, Civil Defence said.

Water still needed to be conserved with a total ban on watering gardens.

About 84 percent of houses could flush their toilets, but 30 percent of those still had sewage going into rivers.

Civil defence pleaded with residents to use toilets sparingly.

Work to clear sewers could take three to four months, Civil Defence said.

No one should swim in rivers or beaches because of raw sewage contamination.

About 17,000 chemical toilets had been delivered to residents and another 20,000 were expected to arrive in coming weeks.

Nearly 2000 portaloos were on hire for the city, with 64 for use at schools.

About 97 percent of schools and 76 percent of early childhood education services were due to be open by Wednesday next week.

The main issue preventing some from opening was a lack of working toilets and drinking water, Civil Defence said.

Nearly 70,600 buildings had been inspected in Christchurch.

- Of 4205 commercial buildings, 832 were red stickered (meaning the building was unsafe to enter).

- Of 4079 buildings in the CBD, 996 were red.

- Of 61,367 residential buildings, 1805 were red.

- Of 941 heritage buildings, 346 were red.

Power had been reconnected to nearly 100 percent of houses and Orion wanted to hear from anyone still without power.

Police would attempt to retrieve cars from the Pavilion carpark on Monday and the Manchester St carpark on Tuesday.

Car owners should bring their keys, ID and proof of ownership to the Barbadoes and Moorhouse intersection at 5pm on each day and register on the police website.

More than 180 people are believed to have died in the quake which struck on February 22.

- Stuff, with NZPA