Doctors are pleading with people who suspect they may have coronavirus to stay home and seek help over the phone rather than visit medical centres.
Doctors say they will have to close entire clinics if people infect them or their staff.
Healthline staff took 2200 calls yesterday about coronavirus.
The phones are being answered 24-7, but some people are not heeding the advice to call.
An Auckland woman who tested positive for Covid-19 on Tuesday night after getting a swab from her GP had walked into the clinic and did not call ahead.
She also took domestic flights to and from Palmerston North before her case was confirmed.
Medical Association chair Kate Baddock said the woman did almost everything wrong in getting treatment.
"We all need to be very, very thoughtful about where we've been, who we've been in contact with, what symptoms we have and not just turn up to medical centres."
Dr Baddock said the risk to medical centre staff and other patients was huge.
"If a practice gets contaminated because somebody comes in with coronavirus and precautions aren't taken because they are at risk and haven't identified themselves as a risk to the practice, then there is a risk that every single person they've been in touch with may need to stand down for two weeks.
"A practice just has to close down and that's an incredibly costly thing to have to do in terms of healthcare."
ProCare clinical director Dr Allan Moffitt told Checkpoint it was still possible that people could walk into a clinic without seeing the sign.
"In that case actually people aren't greatly at risk because the virus - you need close contact over about 15 minutes to be at risk. Obviously different if they're coughing actively in front of people.
"That's why we like them to phone first so we can arrange for a mask to be fitted."
Dr Moffitt said he was surprised and disappointed a medical centre staff member spoke to media.
"They should raise it with management of the clinic, but I can understand all healthcare workers being concerned, because of course this does put healthcare workers in the front line at risk.
"But providing you follow Ministry guidelines and wear appropriate protection, it's quite safe to see patients and treat them.
"The experts are saying there's no risk of contact with somebody who has had exposure to the virus actually spreading the virus.
"The peak time for this virus to spread is really when symptoms appear, then for the next five to six days.
"We're being careful with 14 days, but the peak time is really from when symptoms appear. Prior to that, we don't think there's a high risk people will get infected."
The doctor at the medical centre who saw the North Shore woman with Covid-19 has been put in isolation.
"There's a risk that doctor may actually be infected, but there's no risk of that doctor transferring that infection to anybody else. That's why we put them in isolation so that we know, in case he becomes symptomatic."
Consultations in the car
Rural doctors are preparing to treat people in their cars to limit any possible spread of the illness.
Rural General Practice Network chair Dr Fiona Bolden said: "We try and triage people before they come in the door. We really don't want them coming into the practice and contaminating other people.
"So we will do as we had to do during the measles outbreak - try and see people in their cars and examine them there and make some kind of clinical decision on them from there."
Hamilton GP Rebekah Doran said her practice was looking at virtual consultations. She said a Skype-type of consultation would give doctors the chance to get a virtual assessment of how patients were breathing and how unwell they were looking, so it offered the chance for a better diagnosis than a phone conversation.
Patients who were very unwell would still need to come into the practice so doctors could take their temperatures and oxygen levels, Dr Dorren said.
Royal College of Practitioners medical director Dr Bryan Betty, said while he could understand people's concerns about coronavirus, it was important to keep things in perspective.
"Eighty to 90 percent of people who overseas get coronavirus get better - they recover. They get a mild to moderate cold flu-type illness.
"A lot of people get very few symptoms at all and on the whole they do get better so on the whole while people are anxious they need to be reassured by that fact."