I was in a rural valley to the north of Nelson. I saw this object appear at around 21:57 hrs (9:57pm) NZDST. It wasn't fully dark, but I could see a few of the brighter stars. The stars appeared clearly, but this object initially looked like a small moon behind cloud.

I was looking in a south-westerly direction. The object travelled more or less from west to east (from right to left in the video). It seemed to grow a little fainter in intensity just before it disappeared from my view behind hills. I guess I watched it for maybe two minutes. The object moved steadily and the apparent erratic or up and down movement was caused by me moving my iPhone. I zoomed in (digitally) once the object came into focus.

The object looked more solid in the video. To my naked eye it appeared to be a patch of illuminated cloud with a 'tail'... but the tail was not being dragged behind it, it was 'pushed' on the 'forward' edge of the object.