It originated in the USA and was established in New Zealand in the 1920s. It became really popular in the 1930s when whole theatres, town halls and cinemas could be standing room only for the sessions. Basically it was the singalong around the piano expanded to gargantuan proportions.
The sessions were drop ones at a lunch time and you could bring along your knitting and your lunch and have a good old singalong under the direction of a leader and accompanist. All the old favourites were trotted out and hits from the radio and everyone had a good time. I suppose it was the 1930s version of karaoke.
From today’s perspective it might seem the sort of thing Patsy would be horrified to have accidently enjoyed while sober, but it was considered community building and gave many people something positive in their day during the dark times of depression and war.
As time went by competitions and auctions were added and passing celebrities inveigled into attending. It petered out everywhere but Dunedin. They kept it going to the 1960s).
There is an interesting paper ‘And Everybody Sang’ – Community Singing in Wellington, New Zealand by