Asked why Auckland couldn't move to orange before the rest of the country, Ardern said there was still significant pressure on our health systems.
It was possible to do this in future, she added.
"Auckland has made significant progress ... but we need to look after our healthcare workforce," she said.
Asked about Auckland potentially moving to an orange setting, director-general of health Dr Ashley Bloomfield said the country's biggest city still had a significant pandemic.
"In Auckland, yes, the case numbers are coming down, but there are still several thousand case numbers a day."
He said it was important to protect Auckland's healthcare system, partly because the city had some of the country's most specialised health services.
Bloomfield said there was still a "long tail" of hospitalisations and "Auckland is part of a national hospital network".
"It's less about the case numbers and more about the hospitalisations."
He said it was important to note only about one per cent of cases ended up in hospital, and many others were being cared for at other health providers such as clinics and GPs.
The PM said unvaccinated people and those who had not received booster shots were still disproportionately showing up in hospital with Covid-19.
She said many healthcare workers were themselves infected, adding more pressure to the city's hospitals.
Ardern said it was still possible in the future for some regions to change traffic light settings. So for example, one region might go to orange while others were in red, she said.
"I want New Zealand to be living as normal a life as possible," Ardern said when asked about the traffic light system. "But we want to move carefully."
Masks will still be required in many indoor settings as the red traffic light system stays in place.
Ardern said the Government was mindful of the impact the red traffic light setting had on the hospitality sector.
"It is incredibly difficult on sectors that are particularly reliant on indoor events. Regardless of what setting we're in now, outdoor events can continue."
She said the event management sector was taking a hit, but Government support was available.
"Of all the sectors, they really are the ones that are bearing the brunt."
The PM said other restrictions will end in the next 24 hours.
Vaccine passes are no longer compulsory but some business can still use the passes if desired, Ardern said.
The next traffic light review will be on April 14, she said.
"I know there is an eagerness to move to orange [but] there is still pressure across our hospital network," Ardern added.
The decision comes after nine more Covid-related deaths were reported today, along with 10,205 new community cases.
The deaths reported today take the total number of publicly-reported deaths with Covid-19 to 405 since the pandemic began.
There are 734 people in hospital, including 25 in intensive care, the Ministry of Health said in today's 1pm update.
Today is the last day vaccine passes are mandatory. And vaccine mandates will be limited to the health and disability, aged care, Corrections and border workforce sectors.
The removals of some pandemic health measures and changes to others are based largely on expectations the Omicron wave has peaked.
Meanwhile, Bloomfield said Covid-19 infrastructure could now be applied to other immunisation campaigns ahead of winter.
This would include efforts to get people vaccinated against measles, mumps and rubella.
He said Covid-19 booster rates for elderly people were high for Māori and non-Māori.
"It's the younger age groups where there's still work to do."
Ardern rebukes Russia over atrocities
Ardern addressed claims of Russian troops raping and killing Ukrainians.
"Russia must answer to the world for what they've done," she said.
The PM said Cabinet was considering more steps to help Ukraine.
She said Russia must be held accountable for the invasion and associated atrocities.
When asked if she would call Vladimir Putin a war criminal, Ardern said: "The evidence is there ... That war crimes are being committed by Russia."
Ardern said she was not an international criminal court judge, and it was not her place to affix the "war criminal" label.
The PM said very few countries had recalled diplomats from Russia.
She said many countries had already applied sanctions, tariffs, travel bans, military aid, and equipment to Ukraine.
On diplomatic expulsions, she said: "It is an absolute option for us. It's just that we've prioritised ... more impactful options at this stage."
Meanwhile, Defence Force intelligence analysts had already been sent to Europe, the PM said. She added that the NZDF was well-resourced.
