"Now we need to act globally as the team of 7.8 billion."
There are few other details at this stage – media were given a link to her video and a number of key points just before 5pm today.
But in early March, Ardern and Covid-19 Response Minister Chris Hipkins said any surplus vaccines New Zealand had would be donated "across our wider portfolio to the Pacific and developing countries worldwide".
"We are committed to ensuring that any doses not needed here are put to good use elsewhere," Hipkins said at the time.
In her video, Ardern said: "We welcome efforts to provide more doses of the vaccine to developing countries."
She said as an international community, "we need to do all we can to increase the supply of vaccines".
She said sharing doses was one way this could help.
New Zealand had already donated $17 million to Covax and the 1.6 million doses were fully funded, she confirmed.
A number of other world leaders also made vaccines pledges at the event.
The Netherlands' Minister for Foreign Trade Sigrid Kaag said vaccines were an essential investment to overcome the pandemic.
"We must upscale the availability of vaccines worldwide, ensure that they reach the most vulnerable and that health systems are strong enough.
The Netherlands donated an extra €40 million ($67m) to Covax AMC, in addition to the €52 million already donated.