The mother of the man accused of mowing down pedestrians in Australian, killing five, says she's ashamed to be his mum.

The death toll from the car attack on pedestrians rose from four to five on Saturday night, after a three-month-old baby died in hospital. A 10-year-old girl is also dead, while more than 25 people remain in hospital after being hit when a driver mounted the footpath on Bourke Street in Melbourne and drove into crowds on Friday.

The driver, Dimitrious "Jimmy" Gargasoulas, remains under police guard after being arrested.

His mother, Emily Gargasoulas, told reporters on Saturday she felt sick it was her son.

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"I'm ashamed, I'm ashamed to be his mum," Gargasoulas said. "I couldn't believe it darling, it make me feel sick."

She also apologised, saying she was "so so sorry".

TERRIFIED GIRLFRIEND PUSHED FROM CAR

His girlfriend, Akiir Muo said she was taken hostage by Gargasoulas and thought she was going to die when he started driving erratically.

"I was trying to get out of the car but I couldn't," Muo told reporters. "He had me in the car and he was driving way too fast."

She says he pushed her out of the car and fled from police before he travelled to the CBD.

"I remember the last words that he told me," she said.

"He goes, 'I'm gonna go to the city and I will run a lot of people down'.

"He was saying something about the comets is coming or it's like the end of the world and saying he is the saviour or he's God - all this crappy stuff."

"I'm still in shock: did that really just happen?"

FRACTURED RELATIONSHIP WITH GAY BROTHER

Earlier in the day in a public housing unit on Raleigh Street, Gargasoulas allegedly set upon his brother Angelo with a knife, before evading police for hours.

The young man, who is in his 20s, was allegedly stabbed in the chest and head. He is now fighting for his life.

Angelo's friends said he had a tortured relationship with his brother, who hated the fact that he was gay.

Giuseppe, who became friends with Angelo in 2013 and did not want his surname to be published, said Jimmy refused to accept his brother's sexuality.

"Jimmy never accepted gay people, he was a very homophobic person," he said.

He described his best friend as "outgoing, funny and generous".

"He always had a smile in his face," he said. "He liked to have fun."

The pair quickly became close friends and often went clubbing on weekends. They frequented The Peel Hotel and Baroq and were often mistaken as brothers.

Friends have flooded Angelo's Facebook page to wish him a speedy recovery. "Beautiful angel on earth Angelo, may that sparkle in the person you are ... be one of the driving forces to help heal you physically mentally and emotionally through this dark time," one friend wrote.

Others said they were lost for words.

"So devastated to hear the news. thinking of you, you beautiful soul. if there's anything you've shown me over the years, it's how much strength you possess. Stay strong."

He was rushed to hospital early on Friday in a critical condition and it is understood that he has been placed in an induced coma.