Hollywood superstar Russell Crowe led tributes Saturday to "true gentleman" 74-year-old Sisto Malaspina, a doyen of Melbourne´s thriving cafe culture who was stabbed to death in Friday´s rush hour terror attack.

As crowds gathered at Malaspina´s "Pellegrini" cafe to lay flowers and tokens of remembrance, Australian acting legend Crowe led a flood of tributes online.

"Il mio cuore si spezza" (my heart is broken) he wrote on Twitter in Malaspina´s native Italian.

"I´ve been going to Pellegrini´s since 1987. Never been to Melbourne without dropping in on my man Sisto... My sweet loyal friend, stabbed in the street by a mad man."

Melbourne is Australia´s second largest city, a thriving cosmopolitan metropolis of almost five million people famed for its cafes, bars, restaurants and high standard of living.

Opposition leader Bill Shorten, who is from the city and has been visiting Malaspina´s cafe since his schoolboy days, described the murder of Melbourne´s adopted son as "shocking, unreal and heartbreaking."

"I just saw Sisto on Monday morning. He insisted I try a slice of his almond cake. He´s a Melbourne icon and a true gentleman."

Two other men wounded in the attack are still being treated and are expected to make a recovery.

It was another foreign-born resident of the city, Somali-born Australian, Hassan Khalif Shire Ali, who carried out the deadly knife rampage.

The 30-year-old fled with his family from war-ravaged Somali to Australia as a child in the 1980s.

He was killed on Friday afternoon after driving a 4x4 laden with gas cylinders into the city centre and stabbing three passersby before being confronted by members of the public and armed officers who eventually shot him in the chest.

Unconfirmed local media reports suggested he may also have had problems with substance abuse and mental health issues.

But he was known by intelligence services to hold extremist views and for now the authorities are treating the attack as a terrorist incident.

They have questioned around 35 people who saw the daytime attack, which although crude, was said to have been designed to "cause terror and cause maximum casualties" in the heart of Melbourne.

Armed officers raided two addresses in the west and northeast of the city, linked to the perpetrator´s family and associates, although there is not thought to be an ongoing threat.