Christchurch residents should boil water before drinking, brushing teeth or using in food preparation, the Canterbury District Health Board recommends.

The heath board says residents should bring the water to the boil or, if this is not possible, treat it by adding one teaspoon of household bleach per 10 litres of water and leaving it for 30 minutes.

People are advised to avoid silt brought to the surface through liquefaction, and to wash their hands before preparing food.

The council has asked people to conserve water, and should avoid flushing the toilet.

The health board says people should contact their GP if they need medical assistance. The 24-hour medical centre in Bealey Avenue, the after hours clinic in Moorhouse Avenue and the Riccarton Clinic are open after hours.

All but the most urgent elective surgery has been postponed in Christchurch tomorrow. This includes surgery planned for Christchurch Hospital, Burwood, Southern Cross and St George's Hospital.

All outpatient appointments have also been cancelled at all public hospitals in Christchurch. Planned Caesarean sections at Christchurch Women's Hospital will go ahead, as will all planned radiation therapy and chemotherapy services.

The Emergency Department at Christchurch Hospital is open and able to take patients.

Canterbury District Health Board chief executive David Meates said while no major structural damage to buildings had been identified as of late this afternoon, engineers and maintenance staff were still in the process of checking buildings.

"Unfortunately some of our facilities have sustained damage to infrastructure and are operating on back-up systems. There is no power or water at Burwood and no water at Hillmorton. The lifts are out of action due to water leaking at Princess Margaret Hospital. We have contingency plans for all of these issues and are able to continue to receive and care for patients," Mr Meates said.

"We are aware that some aged residential care facilities have also been damaged and are without essential services."