Australia's biggest private childcare operator, G8 Education, has warned an oversupply of childcare places in the industry won't improve until at least the middle of calendar 2019, with occupancy rates at its 512 centres worsening in every state in the first six months of 2018 leaving it with almost 10,000 unfilled places.

G8 runs its childcare centres under 23 brands that include Headstart, Greenwood, Buggles, Jellybeans, Bambinos, Great Beginnings, Sandcastles, Penguin Childcare and Pelican Childcare, and the poor outlook and a 22 per cent drop in net profit to $23.7 million in the June half caused another big sell-off in the company's shares on Monday.