Melbourne's lord mayor has labelled the actions of climate protesters "unacceptable" as activists halted peak-hour traffic in the CBD for the fifth day in a row.

About 100 protesters gathered at 7.30am on Friday to blockade at the entrance to the global headquarters of mining giant BHP on Collins Street, near Russell Street.

Extinction Rebellion protesters marching on Collins Street. Credit:Zach Hope

Organisers said Friday's action would be more "subdued" than the city-stopping action of previous days. However about an hour into the blockade, protesters stepped onto the road, blocking cars and trams in both directions.

The activists marched west through the middle of the road for about 10 minutes before veering onto the footpath to protest outside the offices of Rio Tinto, near Queen Street.