Opposition Leader Bill Shorten has announced tax cuts for small businesses to hire young and older workers and outlined a $2.3 billion assault on multinationals' tax avoidance as he officially launched the party's election campaign.

Rallying the Labor faithful at the Brisbane Convention Centre, Mr Shorten said voters had a clear choice of three more years of "smug, smirking, unfair complacency" or a better, bolder and more equal future under Labor.