One of the soldiers was killed instantly when an anti-tank rocket hit his armoured vehicle.
The other was on foot when he was hit by gunfire or shrapnel. He died in a helicopter on the way to hospital.
Three other soldiers were seriously injured and are expected to return to New Zealand, and a further three had moderate injuries.
Chief of Defence Force Lieutenant General Rhys Jones said the casualties occurred during "a two to three minute timeframe in that first burst of fire".
Two NDS members died and seven were wounded.
A group of about 17 insurgents carrying dead and wounded were seen leaving the area.
The slain New Zealanders are likely to be named today. They were part of the 19th rotation of PRT troops who arrived last October.
Their bodies are expected to be returned to New Zealand this week.
Relatives of other soldiers in Afghanistan went online yesterday to pay tribute to the men who died.
"I worry about my son every day, but I'm also proud that he is doing a job that ensures most Afghanis know there is humanity in the world," said the mother of one soldier.
Another said: "As a parent of a soldier in Afghanistan, you never stop worrying about them. On the other hand, extreme pride."
Seven New Zealand soldiers have been killed in Afghanistan since 2002, but Saturday's toll makes it New Zealand's worst day in combat since June 18 1970, when infantrymen Lance Corporal Cecil Richard Fisk and Private Leonard Cyril Jones were killed during the Vietnam war.
Mr Key said the loss of the two young men was "an enormous price to pay" as the PRT worked to bring stability to Bamiyan.
"My thoughts are with the family and friends of the two brave soldiers killed and also with the families and friends of those injured."
The Prime Minister said the increased risk in what was already the most dangerous part of Bamiyan province shouldn't alter New Zealand's commitment to keep the PRT in Afghanistan until next year.
"I don't think it argues the case we should stay longer but I don't think that the terrible loss we've suffered also argues we should leave earlier. I think we should just remain on track and continue to do the things we're doing."
Labour Party leader David Shearer, who previously worked for the United Nations in Afghanistan, said the deaths did not mean the PRT, deployed since 2003, should come home early.
"We've got a programme to withdraw over time, and I think that's probably the right way to go.
"Unfortunately it's a dangerous place to work. It's tragic that it's happened towards the end of our programme."
A journalist in Kabul said security in Bamiyan Province had been "deteriorating for quite a while".
"Particularly in the north east, that's where Do Abe is," he told the Herald last night. "That is the place where there's been all the trouble.
"It's a straight out inhospitable place."
He said the area was near where New Zealander Lieutenant Timothy O'Donnell was killed when insurgents ambushed his patrol in August 2010.
"Security in Bamiyan has been deteriorating for a long time. It's been the cause of a lot of concern ... the police commissioner in Bamiyan even called for more support and more assistance."
The family of Lieutenant O'Donnell marked the anniversary of his death on Friday.
Last night his father, Mark O'Donnell, told TVNZ: "It sounds like this happened on the 4th as well, so the 3rd and 4th August are going to be pretty sad times for a number of families now in New Zealand."
Peace activist and former Green MP Keith Locke said that last year, when the PRT handed over security duties in and around Bamiyan city, insurgent activity was low.
But it appeared they were now more active in the north-east of the province where the Taleban and other insurgents had a presence.
"New Zealand has got more involved in the active war, which wasn't like the original PRT mission , at a time when New Zealanders thought that after the departure of the SAS that we had got out of the war and just had this peacekeeping unit in Bamiyan province."
AFGHANISTAN ROLL OF HONOUR
On Saturday two Provincial Reconstruction Team personnel were killed and six wounded during an ambush in Do Abe, in the northeast area of Bamiyan. Here are the other New Zealanders who have died in Afghanistan:
April 2012 - Corporal Douglas Hughes, 26
Corporal Hughes died while off duty at the Romero Forward Patrol Base in Bamiyan Province. The cause of his death has not been disclosed and is being investigated by the army. He had enjoyed life in the army, which he joined aged 17, but he hadn't been keen to serve a second tour of duty in Afghanistan, which he started in September last year.
September 2011 - SAS Corporal Leon Smith, 33
Corporal Smith was shot in the head during an operation in Wardak Province, southwest of Kabul, at a compound suspected of housing Taleban bomb-makers preparing for an attack in the capital. He was posthumously honoured with the Charles Upham Award for Bravery after risking his life trying to save a comrade six weeks before he died. He braved enemy fire when he ran across open ground to reach comrade Corporal Doug Grant and give him first aid.
August 2011 - SAS Corporal Doug Grant, 41
Corporal Grant was fatally wounded during an operation to rescue hostages at the British Council cultural centre in Kabul, which was being attacked by the Taleban. Eight policemen and three Afghan guards were also killed in the raid. Corporal Grant left behind his wife Tina and a daughter, 7, and son, 5. His death was the first SAS fatality in Afghanistan in four deployments since 2001.
February 2011 - PRT Private Kirifi Mila, 27
Private Mila was standing on the turret of a Humvee when it rolled down a 30m cliff near the village of Ferosak in the northeast of Bamiyan Province. Three other soldiers were in the vehicle on a patrol which involved three other Humvees. A military ceremony for Private Mila in Christchurch was cancelled after the earthquake struck the day before.
August 2010 - PRT Lieutenant Timothy O'Donnell
The Provincial Reconstruction Team members were under Lieutenant O'Donnell's command when their patrol was ambushed near the town of Chartok in Bamiyan Province. The lead patrol vehicle was hit by an improvised explosive device, killing Lieutenant O'Donnell and injuring two of his comrades. The pair were honoured for their bravery after they tried to get their dead mate out of the burning vehicle while under intense fire from shoulder-launched rockets and machine guns.
