Council workers and police officers have laid wreaths and flowers outside the Hilton Hotel in Sydney as they remembered three men killed in Australia's first terrorist attack.

Garbage collectors Alex Carter and William Favell were killed on February 13, 1978, when a bomb concealed in a rubbish bin exploded outside the hotel.

Police officer Paul Birmistriw, who was guarding the hotel entrance, was fatally wounded in the attack and died nine days later.

Members of the United Services Union (USU), NSW police, and family and friends gathered on George Street in Sydney's CBD to place flowers in front of the memorial plaque and observe a minute's silence.

USU spokesman Graeme Kelly said Mr Carter and Mr Favell were known to be "larrikins" and "dedicated family men".

A council worker who had worked with the men described them as "good blokes".

NSW Police Association President Scott Weber said Mr Birmistriw had been a "first-class constable".

Those responsible for the bombing, which took place outside the venue for a Commonwealth Heads of Government regional meeting, have never been found.