More than 4000 people gathered at Sydney's Town Hall on Sunday night for a candlelight vigil to remember slain Iranian asylum seeker Reza Berati.

The crowd was addressed by The Chaser's Chris Taylor, and actress Imogen Bailey spoke about her experience on the SBS televison documentary series Go Back To Where You Came From.

Crying out for change: Hundreds take part in the candlelight vigil at Sydney's Town Hall. Credit:Sahlan Hayes

Activist group GetUp said about 15,000 people attended at least 600 snap protests across Australia on Sunday, from Queensland cattle stations to Melbourne's Federation Square.

The protests come days after Mr Berati, 23, was killed and 62 other asylum seekers were injured in violent scenes at the Australian-run immigration detention centre on Papua New Guinea's Manus Island.