An Australian army field hospital is set to be turned into a community health centre as authorities work to prevent a medical crisis in Christchurch.

The 75-bed centre near Cowles Stadium in Aranui will be like the hospitals set up in warzones such as Afghanistan, a Canterbury District Health Board spokeswoman says.

She says it will be self-sufficient and staffed with experienced doctors, nurses and other clinicians from Australia, including six emergency department doctors, 13 nurses, general surgery staff, orthopaedic staff, general trauma, anaesthetists and support staff.

They will help stop the outbreaks of diarrhoea and measles thought to be a serious risk in the wake of Tuesday's 6.3 magnitude aftershock, she says.

"We have seen isolated cases - three or four - of measles already. There is an underlying potential for there to be a measles outbreak. There's a chance of an oubreak of gastro diseases.

"This health centre is in an area where there is a low concentration of GPs. It's like those they set up in fields in Afghanistan. They don't need any input."

It will provide free primary care until Sunday night.

Quake damage to pipes and other infrastructure is still cutting off clean water to more than 40 per cent of Christchurch.

Many residents remain in welfare camps where poor sanitation and cramped living conditions raise the chances of disease outbreak.

A welfare centre previously set up at Cowles Stadium was closed this afternoon due to fears of an outbreak of measles or diarrhea and worries about sanitation.

More than 350 people at the centre were transported by bus to the Rolleston welfare centre, where sanitation is better.

The new army field hospital will ease those concerns by offering free care until Sunday - in line with other primary care centres in the city, a DHB spokeswoman says.

"As the demand for hospital services faces this is our main focus - public health and mental health."

Mental health has also been an issue as anxious Christchurch residents deal with the scars left by the earthquake and the constant stream of aftershocks in its wake.

The Ferry Road Medical Centre in Phillipstown has been helping patients being admitted with shock and anxiety.

Dr Les Toot says the level of distress from Tuesday's aftershock is much greater than experienced after the original 7.1 magnitude earthquake in September.

"We have been through this twice now, but the level of distress and destruction this time is another order of magnitude.

"We had walking wounded coming in initially on Tuesday - people with cuts, minor injuries and things like that. We are starting to get more people with shock coming in and I expect that to increase."

Medical supplies are another challenge in the quake-ravaged city, with pharmacies starting to run out of medication.

The warehouse of one Christchurch medicine supplier had not yet reopened since the quake while the other was only able to provide limited services, community pharmacist Jacqui Lawson told New Zealand Doctor magazine.

Of more than 120 pharmacies throughout Christchurch, 80 are now open.

- with NZPA