There's thought supermarkets could be buying and holding land to block competitors

The Commerce Commission's first annual report on grocery - shows competition hasn't meaningfully improved.

It noted the commission will now focus on land banking - with major grocery retailers owning more than 100 properties that're used for purposes other than retail stores.

Grocery Action Group's Sue Chetwin says some of those will be being used legitimately for things like carparks.

She says the commission wouldn't have mentioned it, unless it had done research to show the duopoly buying land to block competitor supermarkets.