A union representing supermarket workers says investing in systems - not body cameras - will make staff feel safer

Woolworths in Australia's trialing body cameras on shelf-stackers and checkout workers, after a rise in assaults.

Two Countdown staff are among the four stabbed at a Dunedin store yesterday.

All four remain in hospital.

First Union retail secretary Tali Williams says staff would rather see things like security cameras, extra staff and updated technology before bodycams.

She says staff baulk at the idea of wearing cameras - because they're not the ones in the wrong.