The father of a newborn remains in a critical condition after he was beaten unconscious in a violent carjacking - the latest in a spate of attacks to grip Melbourne.

The victim, aged 32, was getting into his car parked on Massey Street, Box Hill South, around 6pm on Saturday when he was set upon.

At least two men attacked him, police said, leaving him bleeding and unconscious before stealing his black 2013 Honda CRV, registration ZRK 896.

Witnesses said one of the attackers jumped in another car and sped away from the eastern suburbs address.