Chrome flying saucer in New Zealand, in 1985

In March 3, 1985, several children were in school in Christchurch (in New Zealand). During lunch break, they have spotted an impressive metallic flying saucer over a field. What is it?

Witness report:

I was a 7 year old at aranui primary school in christchurch, 1985. 2 of us seen it. Featureless Chrome saucer hovering (quite high) above field. Seemed to be observing the children on lunch break. Unsure of elevation or distance as it was in pure blue sky..seemed at least 100m away and maybe 5 meters across but not totally sure. Sat stationary in the sky then dissapeared in an instant. Will never forget.